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Monthly Archives: August 2011

Signing off, for now

August 29th, 2011 - 11:35 am

Via the Catskills region blog The Watershed Post, here’s another incredible video of the epic river flooding caused by Hurricane Irene’s torrential rains:

Dr. Jeff Masters has more on the catastrophic flooding, including some nifty charts showing various rivers’ flood-stage situation. You can find more river flood gauges here. Great stuff from the National Weather Service. Also from the NWS, the final advisory on Irene from the Hydrometeorological Prediction Center includes a ton of eye-catching numbers, with more than 30 locations reporting double-digit rainfall totals. The highest figure is an incredible 20.40 inches in Virginia Beach, Virginia.

With that, I’ll be signing off this blog until the next hurricane threatens, or events otherwise warrant. My role here as PJ Media’s “Weather Nerd” is to provide updates on active, significant tropical cyclones threatening the United States, so Irene’s official demise last night is the blog’s cue to go dormant again for a while. Perhaps I’ll be back in a week or so to talk about Hurricane Katia, presently known as Tropical Depression 12, which formed this morning off the African coast and is expected to steadily strengthen as it churns west over open waters. But then again, perhaps not: there’s an excellent chance “proto-Katia” won’t ever threaten the U.S., per Dr. Masters: “Forecast tracks from the long-range GFS and ECMWF models suggest that Bermuda and Canada might be the only land area threatened by TD 12, but it is too early to be confident of this.”

Anyway, until the next storm threatens, you can follow me on Twitter (though, be warned, my timeline will soon have more talk of college football than hurricanes) or on my personal blog, The Living Room Times.

P.S. The Red Cross is conducting relief efforts in the areas hit hard by Irene. You can donate here. For all the talk about “overhype,” this is a tremendous catastrophe in Vermont, the Catskills, and other regions swamped by flooding rains, so I’d encourage you to help out if you can.

So… who had Vermont in the “State Hardest Hit By Irene” pool?

http://youtu.be/WpRErzxj0Uo

Hurricane Irene made landfall in three places Saturday and Sunday: first at Cape Lookout, North Carolina, then near Beach Haven, New Jersey (ten miles north of Atlantic City), and finally at Coney Island, New York. But this storm won’t be remembered for its impact on the coast. Oh, there was wind annd surge, and there was damage: the Outer Banks Highway was destroyed, Hoboken was flooded, and Lower Manhattan’s seawall was overtopped, among other effects. But when the best an AP reporter can do for a lead quote about a disaster is, “You could see newspaper stands floating down the street,” that’s a pretty good sign it wasn’t exactly the storm of the century — at least not along the coastlines where it hit. Of particular note, flooding in New York was far more shallow and limited than had been feared.

Instead, Irene will be remembered first and foremost for her inland impacts, specifically the catastrophic river flooding now underway in, among other places, the Catskills of New York and, most especially, the last state in the Northeast to make a pre-storm disaster declaration: Vermont.

http://youtu.be/M8zZLyct_D8

(WARNING: Second clip contains profanity.)

The situation in Vermont is pretty terrible, and getting worse as rivers rise. (That appears likely to be the major Irene-related storyline going forward.) Even in New Jersey, where fears of a heavy impact along the shoreline caused Governor Chris Christie to famously advise residents to “Get the Hell off the beach,” the biggest problem was not storm-surge flooding, but river flooding. (“Get the Hell off the riverbank”?)

The inland flooding was no surprise; indeed, I’d been saying for days that it might be “biggest threat of all.” Still, it’s impressive and awful to see the rainfall totals, which are just freaking huge, and the results are devastating in many cases. Irene’s unusually slow movement for this latitude, plus its interaction with a stationary front, have combined to produce a truly historic flooding event that will be the hurricane’s biggest meteorological legacy.

Just as inland flooding was no surprise, the lack of devastating winds was likewise hardly a shocker. We’ve suspected since Wednesday afternoon, and known since Friday morning, that Irene’s winds would not be a huge problem. You can safely ignore the deranged, Drudge-linked conspiracy theory that this 950 millibar storm was somehow a trumped-up tropical depression: plenty of wind observations demonstrate that it was certainly a Category 1 hurricane at landfall in North Carolina, and at least a strong tropical storm in New York and New Jersey. Nevertheless, Irene’s winds were obviously nowhere near what was legitimately feared when it appeared, at midweek last week, that the hurricane might hit North Carolina as a Category 3 or 4, and weaken only to a Category 2 or 3 by its more northern landfalls. But, again, we knew by Friday that the winds would likely underwhelm, and anyone who expected otherwise by Saturday was either not paying attention, being misled by media hype, or both.

What was a surprise was the storm surge — or relative lack thereof. You’ll remember that, even after it became apparent (and was acknowledged in the forecasts) that Irene would make landfall in a weakened state, forecasters were still expecting a storm surge significantly higher than a “typical” hurricane of Irene’s anticipated wind speed. As Dr. Jeff Masters put it Friday morning, “we can…expect a storm surge one full Saffir-Simpson Category higher than Irene’s winds.” Instead, Irene produced a storm surge topping out at roughly 4 feet all up and down the coast — exactly what you’d expect from a storm on the borderline between Category 1 hurricane (4-5 feet) and a tropical storm (0-3 feet). The only reason New York flooded at all was because Irene came in at almost exactly high tide. The tide alone (slightly elevated due to the New Moon), 5 feet above the low water mark, did more than half the work of overtopping those 8-foot seawalls. And they were only just barely overtopped, which is why you saw reporters standing in ankle-deep waters rather than seeing Lower Manhattan transformed into a latter-day Atlantis.

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Why did the storm surge (like so many pieces of economic data recently) underperform expectations? I’m frankly not certain. Remember, I’m not a meteorologist, and I’m certainly not a hydrologist. But I’ve seen this story before, as I pointed out Friday night, when surge fears were high:

But will the surge predictions be borne out? I remember well the predictions of a catastrophic, higher-than-the-winds-would-indicate storm surge with Hurricane Ike in 2008, and those predictions weren’t borne out by the reality (although the surge was plenty bad). Will the same thing happen with Irene, or will the surge meet (or exceed) forecasters’ expectations? I just don’t know.

Ike and Irene were both unusually large storms with unusually deep pressures, whose winds didn’t strengthen as much as expected before landfall, and both resulted in unmet expectations of terrible storm surge. I’m not qualified to opine on what exactly went wrong with these predictions — though if the late Alan Sullivan were still with us, perhaps he’d revive his pimple/hive analogy — nor to suggest changes to the models or anything like that. But it’s certainly worth noting that the last two hurricanes to make landfall in the United States were both huge storms that were expected to cause storm surges well in excess of their wind strength, and both failed to meet the expectations of the computer models. Hopefully the NHC’s post-season analysis of Irene will have some answers on this. Or maybe there’s a Ph.D. thesis in this question for some enterprising meteorology student.

Of course, the big question most people are asking about Irene isn’t why its storm surge was 4 feet instead of 6 or 8, but why it was only a minimal hurricane / strong tropical storm at landfall in the first place. It’s tough for me to get too exercised about that question, since that particular die was cast long ago, between Wednesday afternoon and Friday morning. But anyway, the New York Times does a pretty good job explaining it:

“We were expecting a stronger storm to come into North Carolina,” said James Franklin, chief of the hurricane specialist unit at the National Hurricane Center in Miami. “We had every reason to believe it would strengthen after the Bahamas.”

He added, “What we got wrong was the structure of the storm.”

Forecasters had expected that a spinning band of clouds near its center, called the inner eyewall, would collapse and be replaced by an outer band that would then slowly contract. Such “eyewall replacement cycles” have been known to cause hurricanes to strengthen.

While its eyewall did collapse, Irene never completed the cycle, Mr. Franklin said. “There were a lot of rain bands competing for the same energy,” he said. “So when the eyewall collapsed, there were winds over a large area.”

That led the storm to be much larger, but with the winds spread over a larger area, they were less intense.

All of which brings us to the inevitable questions about “hype.” Was Irene overhyped? Well, yes and no. The fearful possibility of a monster hurricane hitting North Carolina, then taking an exceedingly dangerous and potentially mega-destructive track up the densely populated East Coast, was very real and fully justified as of midweek. And indeed, Irene took precisely the near-worst-case track that was being discussed, with near-worst-case tidal timing for both Chesapeake Bay and New York harbor to boot. That’s 2 out of the 3 necessary conditions to produce a mega-disaster. But all 3 must happen for the “worst case” to occur, and Irene only managed to bat .667. Worst-case scenarios generally require a bunch of bad things to happen in just the right (or rather wrong) combination; otherwise, the feared disaster, no matter how real the threat was, doesn’t come to pass. Here, Irene simply failed to ever became a true “monster” in terms of intensity, and thus her effects were vastly less severe than what they could have been. There was nothing preordained or inevitable about that failure — indeed, the meta-conditions were broadly favorable for rapid strengthening — yet it didn’t happen, demonstrating once again forecasters’ admitted lack of skill at predicting hurricane intensity (in stark contrast to the ever increasing skill, sharply on display here, at predicting hurricanes’ tracks up to 72 hours or so).

As I wrote in my post about “misconceptions,” the mere fact that a worst-case scenario doesn’t occur is hardly proof that it should never have been considered a possibility, or that precautions taken against such a scenario were therefore unwarranted. That’s totally illogical. I’m sure NOAA officials and others would love to have access to the 20/20 Hindsight Computer Model that some commentators seem to possess, but absent that, I believe it was completely justified and necessary to evacuate the folks who were evacuated, given the uncertainties in the forecast at the time decisions had to be made (specifically with regard to the storm surge). It’s the nature of the beast, given the current limits of our forecasting ability, that most “alarms” will be “false alarms.” It’s simply impossible to know with certainty what a storm will do at the time when evacuation decisions must be made, so we have no choice but to “prepare for the worst,” knowing full well that, in most cases and in most places, the worst will not happen. Thus, the fact of a “false alarm,” without more, is not evidence of improper “hype.”

Yet overhype certainly exists, not so much in the forecasts or the precautions, but in the media coverage. “Preparation for the worst-case scenario makes sense,” writes the Telegraph‘s Toby Harnden, “and could have saved hundreds during Katrina. But the worst-case scenario was largely portrayed as inevitable.” That’s a big problem in the early stages of hurricane coverage: the tendency to filter out the uncertainties, and treat the worst-case possibilities as probabilities or near-certainties. This, in turn, feeds into a cycle of self-perpetuating hype, which at some point seems to pass a “point of no return,” after which any walk-back of the doomsday talk is seen as irresponsibly advising people to “let their guard down” — not to mention hurting ratings. That helps cause what I view as the primary problem, which I’ve observed many times over the years: the MSM’s failure to adjust the tone and substance of the coverage once it has become apparent that the worst-case scenario(s), despite having previously been realistic possibilities, have now become unrealistic. In other words, they fail to dial down the hype a notch when the hype, once reasonable, is clearly no longer justified. I tweeted Friday morning about this, stating: “Media must be careful today. Fine line b/w preventing complacency & overhyping a weakened Irene (which breeds cynicism and…complacency). Ideally, you communicate that Irene is a big deal that people should take seriously, but no longer likely to be an apocalyptic hellstorm. But that’s hard to do in practice, especially when MSM weather coverage generally has two settings: 1. #Ignore. 2. #OMGApocalypticHellstorm!”

As I wrote Saturday morning, “we can now be quite confident this won’t be a world-historical disaster… even while being equally confident that it is a force to be reckoned with, and one residents should not blow off. Surely there must be some way to communicate both of these concepts simultaneously.” Needless to say, this properly calibrated, nuanced message didn’t win the day. Instead, many folks apparently continued to believe they were indeed dealing with an apocalyptic hellstorm, a world-historic disaster of the sort that had been, in reality, pretty much off the table since Thursday or Friday. Why did they believe this? Because many folks in the media didn’t convey otherwise, even though the National Hurricane Center had made the diminished threat clear. (It’s not like I was going out on a limb. I was just relaying the publicly available forecast information.)

This pattern is dangerous, because it can breed both complacency and arrogance — the latter exemplified by Anne Thompson’s comment on the NBC Nightly News that New Yorkers had gained their “swagger” back because “New York took the best that Irene could give, and made it through.” That statement might make sense, if Irene had given New York anything close to “the best [it] could give.” But Irene didn’t do that. It’s absolutely critical to understand that this was nowhere near the worst-case scenario for NYC & environs, thanks to Irene’s limited strength. That scenario will occur come to pass someday; it just wasn’t today, thank goodness. But my fear now is that, when the eventual day of reckoning comes, folks won’t take it seriously because “they said that about Irene too.” Complacency caused by media overhype can kill, just as surely as complacency caused by people “letting their guard down” due to underhype. Finding the proper balance is very tricky, and impossible to do perfectly — but the media certainly needs to do better.

Heck, maybe the “day of reckoning” will come sooner rather than later. Let’s hope not. But computer models are calling for “Invest 92L,” a tropical wave off Africa, to eventually become Hurricane Katia (the replacement on the six-year rotating name list for the retired name “Katrina”), and some models think it will eventually menace the East Coast in about two weeks’ time, potentially around the weekend of 9/11. (FSU meteorologist Ryan Maue, he of the beautiful computer model graphics, referred to a Saturday-night model run as the “oh s**t, not again” forecast.) Other models think it will slide harmlessly out to sea. Here’s what the European model predicts for September 7:

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It’s way, way, way, WAY too early to tell what “proto-Katia” will do, or to worry about this hypothetical storm. But it just goes to show how active the tropics are right now.

Irene Makes Landfall in New York City

August 28th, 2011 - 6:41 am

[NOTE: For the very latest on Irene, check my Twitter feed.]

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Hurricane Irene came ashore this morning over Coney Island, New York, weakening to a tropical storm as it did so. I’ll save any damage assessment until later, as early impressions are often wrong. But it’s safe to say that New York is very, very lucky Irene didn’t intensify into a Category 4 monster south of the Carolinas, as had been reasonably expected by forecasters before the storm’s inner core structure fell apart Wednesday/Thursday and unexpectedly never recovered. Irene’s track (and timing, in terms of high tide) ended up being pretty darn worst-case for highly vulnerable NYC, but thankfully, its intensity wasn’t. Hence, the storm surge peaked around 4 feet — bad enough to cause significant flooding, but seemingly not catastrophic — and the sustained winds probably topped out at high-end tropical storm force. Had this hurricane become a monster down south, it would have had a much bigger storm surge all throughout its life, and its winds would have had a long way to go in order to weaken to tropical storm force. It’s very plausible New York could have been hit by a Category 2 hurricane in that scenario, maybe even a low-end Category 3, and there’d be no discussion of “overhype.”

More later.


Above: Wind-velocity Doppler radar showing the wind direction shifting as Irene hit NYC.

Irene: Watching the Surge

August 27th, 2011 - 7:53 pm

[NOTE: For the very latest on Irene, check my Twitter feed.]

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As I’ve said repeatedly, the big storyline with regard to Hurricane Irene’s coastal impact isn’t the winds, but the storm surge. Even if Irene weakens to a tropical storm overnight, as she may, what we really need to watch is how high the surge gets. Of particular significance, New York’s subway system will reportedly flood if the storm surge is more than 3 to 4 feet above the already astronomically high tide tomorrow morning.

With that said, check out this NOAA chart, updating in real time (or close to it), of the water level at The Battery in Lower Manhattan:

Click on the chart for a larger version. The blue line is the expected, “normal” water level, as the tides come in and out. Actually, “normal” isn’t quite right, since we’re dealing with astronomically high tides, thanks to the New Moon. But anyway, the blue line is what the tides would be without Irene.

The red line is the actual water level. When you see the red line not declining, or only declining slightly, while the blue line is going way down, that’s bad news. It means the storm surge is preventing the tide from going out, so the next high tide will likely be much higher (assuming the surge is still present when the tide comes in).

But the one to really watch is the green line. This is the “residual” level, the difference between the red and blue lines. Basically, the green line is the storm surge. So, for instance, if the red line is declining as the tide goes out, but not as much as it “should” be declining (as in the scenario just discussed), that will cause the green line to go up.

Low tide is at 2:14 AM. High tide is at 8:07 AM. Irene’s expected closest pass is expected at around 8:00 10:00 AM — so it’ll be very nearby at high tide. Awful timing. (Once the storm passes, the winds shift to blowing offshore, and the storm surge begins to fall away. See, for instance, Yorktown, VA. But in NYC, that likely will not happen until after high tide.)

Oh, and wave heights, I should note, are on top of the surge.

Regarding the subway, if you want to get a little more into the weeds… based on what Dr. Jeff Masters has written about this, it appears the seawall that protects the subway is approximately 8 feet above the “MLLW,” or “Mean Lower Low Water” level. An average high tide is roughly 4.5 feet above MLLW. The New Moon adds another 0.5 feet to tomorrow’s high tide. That leaves a 3-foot margin for error, give or take a few inches. So a surge of greater than 3 feet at high tide would likely flood the subway, unless Dr. Masters is wrong or I’m missing something here.

Moreover, if the surge reaches 4.5 feet at high tide, here are some of the areas that would potentially be underwater at high tide, according to Climate Central:

graphics_irene_large1-600x337

Note: I’m not sure if that map takes into account seawalls and such. So take it with a grain of salt, giving you a general idea of the amount of territory at risk, but not necessarily a precise block-by-block map of who’d be flooded.

The Weather Channel’s Bryan Norcross just broached the possibility of a 7- or 8-foot surge. I have no idea what that would do, beyond a vague assumption that it would be very bad. It seems high to me — but then again, New York harbor is acting like a giant funnel, so maybe it could happen. Hopefully not.

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Anyway, that’s the situation with New York City. But of course, Gotham isn’t the only place at risk. And I thought it might be helpful to try and collect all the relevant tidal information in one place. NOAA maintains an excellent site where you can view tidal gauges for a variety of locales all around the country, including up and down the East Coast, but they’re all on individual pages. It also has a great “QuickLook” page where you can view this data, and more, about Hurricane Irene. But for viewing the critical storm surge data, and only that data, all in one place, I’m taking the liberty of combining a bunch of these charts in this post, on the next page.

One big caveat to all of this: I’m not a meteorologist, but I at least know a fair bit about meteorology from a layman’s perspective. Hydrology is a different story. I am definitely not a hydrologist, and I can’t even pretend to play one on the Internet. So while I think I’m getting the basic facts right here, it’s possible I’m making some mistakes in interpreting these charts. If someone more knowledgeable than I sees an error, please let me know!

Anyway, on with the tidal gauges:

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Irene, and its storm surge, head north

August 27th, 2011 - 1:29 pm

[NOTE: For the very latest information, check my Twitter feed.]

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After wobbling a bit to the “left” after landfall at Cape Lookout, North Carolina — seeming to perhaps imply, for a few hours, the possibility of a track further inland than expected — Hurricane Irene has wobbled back to the “right,” and is about to emerge back over open waters:

Mind you, hurricanes always wobble, so this doesn’t mean that it’s suddenly going to go out to sea or anything. Think of it as a correction to the previous wobble, putting the storm back on track. I’d say Irene is still very much on course for the expected grazing/raking of basically the entire mid-Atlantic coast.

Speaking of which, check out this tidal gauge chart from Yorktown, VA, near the mouth of Chesapeake Bay:

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The blue line is the expected, “normal” water level, as the tides come in and out. The red line is the actual water level. The green line is the “residual” water level, showing how much above normal it is. The concerning part is how, since the last high tide around 8am local time (12:00 GMT on the chart), the tide has been unable to go out. This is a consequence of Irene being so large and slow-moving, so its winds pile water onto the same shorelines (and into the same bays) for hours and hours and hours, throughout an entire tidal cycle or even multiple cycles. Anyway, although Yorktown is presently at low tide, the water is just as high as it was at the last high tide — and rising. The next high tide is four hours away, give or take, and so is the center of Irene. With onshore winds pounding the bay as the storm approaches, both the red and green lines are about to start really climbing.

A similar problem is expected to occur at the next tide cycle in the New Jersey and New York area. Hence those evacuations. It’s not about the wind, folks, it’s about the water. More tidal gauges here and here.

Worth watching: The Battery, NY tidal gauge. Next high tide is at 7:30 PM local time, and then critically, the next low tide is at 2:14 AM. Watch how much the tide goes out (or doesn’t) between 7:30pm and 2:14am. Then comes the critical high tide, at 8:07 AM, when the storm’s center is forecast to be very, very nearby. If New York is going to flood, that’s when it will happen. Just 4 or 5 feet above the “normal” high tide (i.e., the blue line) — which is actually already elevated due to the New Moon — might do it.

As long as I’m geeking out with charts and graphs (hey, they don’t call me the “Weather Nerd” for nothing), here’s another fun chart, showing pressure and wind at Cape Lookout as the storm made landfall:

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The wind speeds do not actually reach hurricane force (74+ mph), instead topping out around 67 mph. That might lead one to believe that Irene was actually a strong tropical storm at landfall in North Carolina… but that’s hard to believe, with such a low pressure reading (952 mb is usually more associated with a Category 3 hurricane), and in any event, there are wind reports from elsewhere in the Outer Banks that are stronger. For instance:

The Cedar Island Ferry Terminal measured sustained winds of 90 mph, gusting to 110 mph at 7:19am, and a trained spotter on Atlantic Beach measured sustained winds of 85 mph, gusting to 101 mph at 10:35 am. The Hurricane Hunters measured 80 mph winds over water at the time of landfall.

Interestingly, and perhaps somewhat relatedly, the previously linked radar animation seems to show Irene at its strongest several hours after landfall. The after-the-fact meteorological analysis of this storm will be very interesting.

For now, looking forward, nothing has really changed. Irene is still headed toward the northeast megalopolises, still a Category 1 hurricane(-ish), still a moderate wind threat, still a major storm surge and inland flooding threat. On the latter point, here’s a predicted rainfall map:

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And, per Dr. Jeff Masters, radar verifies huge rain totals falling in the storm’s path. That’s going to be a big, big deal.

Everyone should be pretty well done with preparations by now. Time to hunker down and hope for the best!

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Hurricane Irene made landfall this morning near Cape Lookout, North Carolina, as a Category 1 hurricane with maximum sustained winds estimated at 85 mph.

There is some indication on satellite and radar that Irene may actually be getting slightly better organized at this hour — the Outer Banks don’t provide much real land interaction, and the hurricane is still drawing plenty of moisture from the Atlantic, so that’s possible — but I’ll believe it when it’s verified. There have been a ton of false alarms over the last few days with this storm seemingly trying to get organized, so I’m not going to jump at every radar or satellite blip that suggests “tightening” or intensification. In any event, it’s hard to see Irene getting significantly stronger at this point. If she’s tightening, maybe she’ll hold together as a minimal hurricane through landfall in Long Island, instead of weakening to a strong tropical storm. That’s probably the realistic worst case at this point.

Regardless, the general parameters of this situation seem quite clear, and basically unchanged since yesterday. Wind damage will occur, particularly with trees and branches, but the winds will not be catastrophic by any means. In terms of wind, this may feel to a lot of folks like a strong Nor’easter. Power outages will likely be widespread. Inland flooding will be a big, big deal — if there are deaths in this hurricane, aside from the odd Darwin Award-winning surfer or beachgoer, that’s where they’re likely to come from. The severity of the storm surge is the big open question; we’ll see. (Watch the tidal gauges.) Residents in low-lying areas in evacuation zones should continue to assume the (realistic) worst, and should already be out or rapidly getting the Hell out. Bottom line, Irene is a big storm to be taken seriously, and it will cause a stormy weekend and plenty of damage, but this is by no means the worst-case scenario for NYC and the northeast — and to the extent the media or government is pretending otherwise, they need to ramp down the hype, for the sake of avoiding complacency about the next storm. Fear of a calamity was fully justified 24-36 hours ago, but we can now be quite confident this won’t be a world-historical disaster… even while being equally confident that it is a force to be reckoned with, and one residents should not blow off. Surely there must be some way to communicate both of these concepts simultaneously.

UPDATE: Irene, and its storm surge, head north

[NOTE: For the very latest information, check my Twitter feed.]

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For a variety of practical reasons, I’ve had to focus my Irene-related energies exclusively on Twitter all day, and haven’t posted an update here in more than 12 hours. But, truth be told, I don’t have much new to say about the storm, meteorologically at least, that I didn’t say this morning.

irene-windfield-friIrene is continuing to move north (now slightly NNE, as expected) on the predicted track, with the computer models now tightly clustered around a path that, after walloping North Carolina’s Outer Banks, should take the storm’s center right up the coast, directly along the shore of the Delmarva and New Jersey, and then into (most likely) west or central Long Island. As for the storm’s intensity, it’s now down to 100 mph, a minimal Category 2, and re-strengthening still looks unlikely. After hitting North Carolina tomorrow morning at roughly its current intensity, Irene is still expected to start weakening more steadily, and hit the Mid-Atlantic and New York/New England as a Category 1 or strong tropical storm.

Really, at this point we’re in the stage of waiting and watching what the actual impacts will be. We can be fairly confident that the flooding rains will be severe, and that power outages will be widespread — but that otherwise, the winds won’t cause much severe damage beyond North Carolina (although the duration of sustained tropical-storm force winds will create some problems). The big question is how bad the storm surge will prove to be. (Speaking of which, you can watch various NOAA tidal gauges in Irene-affected regions here.)

It’s expected that the sheer size of Irene, coupled with astronomical high tides, coupled with the storm’s slow movement (meaning that, at any given location, winds of at least tropical-storm force may extend through an entire tide cycle or two), will result in a greater surge than you’d expect given what Irene’s wind speed will be. This expected surge is seen as a major threat to various coastal locations, including low-lying areas in New York City, as well as to the NYC subway system, which is why New York ordered an unprecedented mandatory evacuation of “Zone A” and all of the Rockaways, and announced it would shut down its entire transit system starting Saturday at noon. (It also led to New Jersey governor Chris Christie’s epic rant at dawdling beachgoers, in the YouTube clip at the top of this post.)

But will the surge predictions be borne out? I remember well the predictions of a catastrophic, higher-than-the-winds-would-indicate storm surge with Hurricane Ike in 2008, and those predictions weren’t borne out by the reality (although the surge was plenty bad). Will the same thing happen with Irene, or will the surge meet (or exceed) forecasters’ expectations? I just don’t know. I certainly continue to strongly urge everyone to assume the predictions are true, and prepare for the worst. But I’m really very curious to see what will happen. Will the subways flood? Will the airports and the Rockaways be submerged? Will much of Hoboken be underwater? We’ll find out soon!

In the mean time, some smart decisions were made today. Mayor Bloomberg proved he’s not an idiot — well, at least not on this issue — and that he’s no Ray Nagin (who, incidentally, is apparently MSNBC’s new disaster preparedness expert), by ordering the mandatory evacuation around midday today, instead of tomorrow morning as he’d foolishly planned. Also, the NFL preseason game between the Jets and Giants, which had been absurdly scheduled to go forward tomorrow afternoon amid evacuations and transit shutdowns, has been rightly postponed to Monday evening. Sanity prevails over indefensible idiocy. Hooray!

Of course, the biggest decisions are the ones to be made in the next 12-18 hours by individual people in the path of this storm, deciding whether to take it seriously and what precautions to take. Bottom line: take it seriously. If you’re in an evacuation zone, leave. If you’re not, hunker down and make sure you have everything you need for a potentially long and unpleasant aftermath. Maybe some of the evacuations will prove, with the benefit of hindsight, to have been unnecessary, and maybe some of the hurricane-kit items won’t be needed, but it’s far better to be safe than sorry, especially when dealing with something as difficult to predict as a hurricane. So, as I keep saying on Twitter, take Irene seriously and #PREPARE.

And remember that, if the worst doesn’t happen, that doesn’t mean the storm was “overhyped.” It means that, of the various plausible scenarios that presented themselves to forecasters, we ended up experiencing one of the numerous “less bad” scenarios. Worst-cases are always unlikely, and most hurricane “alarms” end up being, at least in part, “false” alarms. That’s just the nature of the beast, as I wrote in my “misconceptions” post. It doesn’t mean we shouldn’t prepare for the worst — every time. Hope for the best, prepare for the worst. There’s just no other choice. That’s exactly what people should keep doing now.

Oh, and get the Hell off the beach.

[NOTE: For the very latest information, check my Twitter feed, and the other sources listed below.]

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As of 11:00 AM EDT, Irene’s maximum sustained winds are down to 105 mph, making it a mid-range Category 2, and the hurricane is officially no longer expected to re-strengthen at all. The forecast calls for the status quo through landfall in North Carolina, followed by weakening to 100 mph (low-end Cat. 2) and then 85 mph (mid-range Cat. 1) as the storm moves up the coast toward Long Island. If the track shifts slightly left, weakening would presumably happen faster over land. Either way, NYC & environs are now likely looking at Category 1 winds at most. (And maybe not even that, as Dr. Jeff Masters explains below.)

As I just tweeted, Irene is reminder of how much mystery remains in the science of hurricane intensity forecasting. All of the meta-conditions were ripe for her to become a monster. But disruptions in the storm’s own internal structure — the least well understood part of a hurricane — have prevented Irene from getting her act together well enough to take full advantage of the favorable environment. Those fears of a Category 4 monster were not unjustified hype. There was every reason to believe they’d be realized. They just…weren’t. So it goes with hurricanes sometimes. (Phew!)

Anyway, although we can now almost assuredly remove “world-historical disaster” from the list of realistic possibilities, this remains a serious situation for North Carolina and for the Mid-Atlantic and Northeast, including the New York area. Dr. Jeff Masters elaborates:

With its eyewall collapsed and just 24 more hours over water before landfall, it is unlikely Irene will have time to build a new eyewall and intensify. The storm is too large to weaken quickly, and the best forecast is that Irene will be a Category 2 hurricane at landfall in North Carolina on Saturday, and a rapidly weakening Category 1 hurricane at its second landfall in New England on Sunday. However, since Irene is such a huge storm–tropical storm force winds extend out up to 290 miles from the center–it has set a massive amount of the ocean’s surface in motion, which will cause a much larger storm surge than the winds would suggest. At 9:30am EDT this morning, a wind analysis from NOAA/HRD indicated that the potential storm surge damage from Irene rated a 5.1 on a scale of 0 to 6. This is equivalent to the storm surge a typical Category 4 hurricane would have. While this damage potential should gradually decline as Irene moves northwards and weakens, we can still expect a storm surge one full Saffir-Simpson Category higher than Irene’s winds. Since tides are at their highest levels of the month this weekend due to the new moon, storm surge flooding will be at a maximum during the high tidal cycles that will occur at 8 pm Saturday night and 8 am Sunday morning. At those times, Irene is expected to be near the NC/VA border, then close to Long Island, NY, respectively. Thus, storm surge damage rivaling that experienced during Hurricane Isabel in 2003 is likely in northern NC, southern Maryland, and up Chesapeake Bay on Saturday night. It looks like Irene will pass New Jersey during low tide, which may limit the storm surge inundation to 3 – 6 feet there. Coastal New England from New York City to Massachusetts may also see storm surges characteristic of a Category 1 hurricane during Sunday morning’s high tide, even if Irene has weakened to a tropical storm. I continue to give a 20% chance that a storm surge high enough to over-top the Manhattan flood walls and swamp the New York City subway system will occur on Sunday.

Significant wind damage, outside of North Carolina, is unlikely, Masters explains: “the eye of the storm will be just offshore, and the I-95 corridor from Virginia to New Jersey will be on the weak (left) side of the hurricane,” so with “almost all of the hurricane’s winds are on the right side of the storm…there will be likely be no hurricane-force winds on the left side of Irene” by the time it reaches Virginia and points northward. “Sustained winds should stay below 74 mph (hurricane force), and wind damage will be similar to that wrought be some of the strongest Nor’easters of the past 20 years, from Virginia northwards to New York City.” That said, tree damage will be much worse than in a Nor’easter, because “the trees are in full leaf during hurricane season, and catch the wind much more readily than during the winter. Tree damage will very heavy, and we can expect trees in regions with saturated soils will fall over in high winds onto power lines. Irene is likely to cause one of the top-five most widespread power outages in American history from a storm.”

Meanwhile, the biggest threat of all may be inland flooding:

In addition to storm surge, flash flooding and river flooding from Irene’s torrential rains are the main threats. The hurricane is expected to bring rains in excess of 8″ to a 100-mile-wide swath from Eastern North Carolina northwards along the coast, through New York City. The danger of fresh water flooding is greatest in northern New Jersey, Southeast Pennsylvania, and Southeast New York, where the soils are saturated from heavy August rains that were among the heaviest on record. New Jersey has had its 6th wettest August on record, with most of that rain falling in the past two weeks. Expect major river flooding throughout New Jersey the Delmarva Peninsula, and regions near New York City, as Irene’s rains run off the saturated soils directly into the rivers. In general, the heaviest rains will fall along the west side of the hurricane’s track, and the greatest wind damage will occur on the east side.

Also, the possibility of re-strengthening, although no longer expected, cannot be totally ruled out until Irene hits North Carolina. So stay tuned, and continue to prepare for the worst.

I won’t be able to update this blog as much today, but stay tuned to my Twitter feed for the latest. Other sources for information:

• The National Hurricane Center, with major updates, including new forecast tracks, coming out at 5:00 and 11:00 EDT (AM and PM), and minor updates at 2:00 and 8:00 (again, AM and PM).
• For computer model graphics, Ryan Maue’s Twitter feed and his excellent website.
NOAA satellite images
Doppler radar images
• Weatherblogger Dr. Jeff Masters
• Weatherblogger Eric Berger
• Weatherblog FLhurricane.com

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The answer to the question I posed before going to bed last night is… no. Irene’s winds didn’t “catch up” with the her barometric pressure overnight, turning the storm into a picture-perfect monster. Instead, she actually weakened slightly, from 115 to 110 mph — and she’s running out of time to re-strengthen. It looks like my post yesterday afternoon about a weaker Irene, which I almost immediately walked back, may have been right after all. (But DO NOT GROW COMPLACENT, folks in Irene’s path. Continue to prepare for the worst. The potential impacts of this storm — even if she never gets stronger than 110 mph again — are still, as a certain resident of Delaware would say, a big f***ing deal.)

From the 5am NHC discussion:

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE INTENSITY OF IRENE IS NOT QUITE AT MAJOR HURRICANE STATUS. …

WATER VAPOR IMAGERY AND ANALSYES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SUGGEST THAT IRENE IS ENCOUNTERING LIGHT TO MODERATE SOUTHWESTERLY VERTICAL WIND SHEAR. THIS… ALONG WITH THE CURRENT CYCLONE STRUCTURE AND DRY AIR ADVECTING TOWARD THE HURRICANE IN WATER VAPOR IMAGERY… ARGUE AGAINST SIGNIFICANT STRENGTHENING… AND INDEED THE INTENSITY GUIDANCE SHOWS LITTLE CHANGE IN STRENGTH BEFORE LANDFALL. ON THE OTHER HAND…THE EYEWALL CONVECTION IS CURRENTLY STRONG…AND THE SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK ARE 28-29C. THIS SUGGESTS SOME MODEST STRENGTHENING IS POSSIBLE. IRENE IS EXPECTED TO BE NEAR THE CATEGORY 2/3 BOUNDARY WHEN IT REACHES THE VICINITY OF THE OUTER BANKS…AND SLOWLY WEAKEN AFTER THAT. AFTER MOVING INTO NEW ENGLAND…IRENE SHOULD WEAKEN QUICKLY AS IT UNDERGOES EXTRATROPICAL TRANSITION.

Irene is now expected, once again, to peak at 120 mph, and maintain that intensity for just 12 hours or so. That could change, in either direction, but the bottom line is that the odds of this hurricane becoming a high-end Cat 3. or even Cat. 4 — which would in turn increase the odds of Cat. 2 impacts in the northeast, and worsen the storm surge wherever Irene hits — are decreasing.

One major caveat: Irene still has to cross the Gulf stream. The NHC and the computer models know this, of course, and it’s probably part of the reason why they’re expecting re-intensification from 110 to 120 mph. Still, those deeply warm waters can affect hurricane intensity like jet fuel on a fire, and it wouldn’t be shocking if Irene experiences an unexpectedly pronounced spike in strength as she traverses them.

In any event, regardless of her exact intensity, folks in Irene’s path should continue to take it very seriously. This is a still a huge, very serious hurricane. There will be major wind, storm surge, and rain impacts all across the Carolinas, mid-Atlantic and northeast this weekend. PREPARE! And if you’re advised or told to evacuate, EVACUATE! Far better safe than sorry when forecasts are so uncertain and the potential for disaster is so high.

Editor’s Note: Don’t miss “Personal Responsibility: Irene Prep.”

Will we wake up to a monster Irene?

August 25th, 2011 - 11:20 pm

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Hurricane Irene is “still” a minimal Category 3 — really, she’s back up to true Cat. 3 status after an unacknowledged weakening to Cat. 2 strength that lasted most of the day — and her barometric pressure is down to 942 MB (or, according to one recon report, 936 MB). Such pressure readings are usually associated with a Category 4 hurricane, i.e. with winds of 131 mph or greater, yet Irene is stuck on 115 mph. This means one of three things. Either:

1. Irene’s winds are about to “catch up” with her pressure. We see this all the time. She’ll ramp up overnight, and we’ll wake up to a terrifying-looking monster storm menacing the coast, with a perfect eye and 135+ mph winds. Or:

2. Irene isn’t getting stronger, in terms of wind speed. Instead, she’s getting bigger. Her wind field is spreading out, and the low pressure is basically supporting that expansion instead of supporting much strengthening. We’ve seen this before, e.g., with enormous Ike, which was a 944 mb Category 2 with 100 mph winds at one point. Or:

3. Some combination of the two.

We’ll find out soon enough which it is. Meanwhile, the storm’s track remains completely uncertain. North Carolina is clearly going to get walloped, but after that, Irene could go just about anywhere along the I-95 corridor. She could track inland, over Virginia and the Chesapeake region, then come at the northeastern corridor cities with its center over land; she could hug the coastline and deliver heavy blows to Delaware Bay and the New Jersey shore; or she could track right over NYC, or Long Island; or she could go further east toward Cape Cod & environs. And she could be a Category 2, a Category 1, or even a tropical storm. We just don’t know yet.

Meanwhile, regardless of Irene’s exact position and strength at landfall, inland flooding is going to be a huge problem. We’re talking about a foot or more of rain on already saturated ground.