[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:

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:

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:

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

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[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 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.

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[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.”

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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.

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On Saturday night, August 27, 2005, during the early stages of my & my old blog’s 15 minutes of fame as Hurricane Katrina neared the Gulf coast, I published a blog post titled “The mayor of New Orleans is an idiot.” I wrote:

I can’t emphasize enough what a bad decision I think it is for New Orleans Mayor Ray Nagin to delay the mandatory evacuation order until tomorrow morning. … Landfall is expected to occur around midday Monday. So by waiting until tomorrow morning, Mayor Nagin will be giving people scarcely 24 hours to get out. Perhaps he’s hoping to ease the evacuation traffic jams by starting things off with a trickle, but that’s awfully risky. Will Ray Nagin go down in history as the mayor who fiddled while New Orleans drowned? Could be.

Two days short of six years later, with a big-time hurricane hurdling toward a Sunday strike on his city, is New York City Mayor Michael Bloomberg making the same mistake? He has announced that he will wait until Saturday morning to decide whether to order a mandatory evacuation of the “Zone A” low-lying areas that are home to roughly 250,000 people. So, like Nagin, he’ll be ordering an evacuation on the very day before the storm’s landfall or closest approach, and with perhaps 12 hours or less before conditions begin to deteriorate. That seems pretty foolish. Heck, I thought late Friday was pretty late to get started. Saturday morning? Really?!

Of course, some things set Bloomberg’s situation apart from Nagin’s. First of all, his city doesn’t sit below sea level, and isn’t liable to become a total post-apocalyptic hellhole for weeks after a direct hit. Don’t get me wrong, the aftermath could be quite unpleasant — but, as I said before, not so bad that all 8 million New Yorkers need to leave. (By contrast, all of New Orleans really should have evacuated.) So, given the smaller number of people involved, perhaps Bloomberg’s planners have assured him that 12-18 hours is enough time. I’m skeptical, but certainly, they have access to information I don’t, and hey, perhaps they’re right. Maybe starting with voluntary evacuations now — and letting the surrounding vulnerable coastal areas, e.g. in Long Island and New Jersey, evacuate first — will make things easier and safer. Maybe.

I hope, though, that Bloomberg & co. have taken a few things into account. First, an order mandating that 250,000 people evacuate won’t merely put 250,000 people on the roads. A lot of people on higher ground, who don’t technically need to evacuate, will undoubtedly feel that the mayor’s evacuation order is their cue to leave as well. When the mayor tells a good chunk of the city to Get The Hell Out, that’s going to be jarring and frightening, and lots of people will freak out and leave. Nobody can know exactly how many will do this, but I bet the number is non-negligible. And the longer New York waits, the better the odds of roads being overwhelmed, leading to the nightmare scenario of folks stuck on the roads during a hurricane. (“But this is New York!” you protest. “People won’t take the roads, they’ll take mass transit!” No, they won’t.)

Second, what if Irene intensifies more than expected, and suddenly a Category 2 landfall near NYC is in play? That would greatly expand the amount of territory, and thus presumably the number of people, affected by an evacuation order, since it would require “Zone B” to get out too. You certainly wouldn’t want to wait until Saturday morning to start evacuating both zones.

Third, what about people in vulnerable high-rises? Usually, the saying is “run from the water, hide from the wind,” but depending on the forecast track, folks in residential high-rises may well need to run from the wind. Is that factored into the evacuation timetable, too?

(Personally, for what it’s worth, if I were in a vulnerable part of NYC – or anywhere else in Irene’s path – I would make a decision right now about whether to evacuate, assuming the worst-case track. If the answer is “yes,” I would leave tonight, or first thing tomorrow. I’d beat the rush, avoid the traffic jam, and get the Hell out of Dodge Gotham. But that’s just me.)

Bottom line, I’m not prepared to outright condemn Bloomberg here, because the situation is a little murkier than it was with New Orleans, and I know I don’t have access to all the information that the decision-makers do. But I am highly, highly skeptical that this delay was the right call.

One thing I know is the wrong call is the decision to play the Jets-Giants preseason NFL game on Saturday, albeit with an accelerated kickoff time of 2pm instead of 7pm. Playing this game at all on Saturday is absolutely absurd, full stop. Saturday should be a day for evacuations and last-minute preparations, and that’s it. Adding pre- and post-game traffic to the evacuation traffic is beyond irresponsible, and even worse is the message that this sends to the public: that it’s business as usual, the hurricane is no big deal, let’s go watch a football game!

Look, I love football. But let me be clear. Going forward with the Jets-Giants game on Saturday is an unbelievably terrible, inexcusably irresponsible, utterly indefensible decision, and it must be overturned. I strongly urge Andrew Cuomo, Chris Christie and Michael Bloomberg to use the power of their offices to convince the NFL to call off this game, and if the NFL refuses to cooperate, I urge them to publicly shame the league into doing so. Anything less would be a failure of leadership. It’s an utter absurdity that going forward with the game is even being contemplated under the circumstances.

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I should really stop trying to blog potential good news. First it was “the trend is your friend” about the eastward forecast trend, which promptly reversed itself. Now I just posted about the possibility Irene might not fully get her act back together — only to see her on satellite (visible, infrared, water vapor), appearing to get her act back together.

We’ll see what happens, but I’m back to thinking my original prediction, last night, is more likely to prove right: “The hurricane doesn’t yet have the classic appearance of a monster storm on satellite, because she probably just went through, or is going through, an eyewall replacement cycle (the details are a bit murky at the moment). But it’s quite likely she will develop that classic appearance in the next 24 hours or so. When she does, people will suddenly start to panic.”

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I will start this post as I’m going to end it: with a caveat. Hurricane Irene is still a huge threat to millions of people. It could still be a disaster, maybe even a world-historical catastrophe. Everyone in its path should continue to take it EXTREMELY seriously, and PREPARE NOW for a major, destructive direct hit.

Having said all that…

The 5:00 PM National Hurricane Center discussion gives some reason to hope that Hurricane Irene — while still dangerous — may not prove to be quite the monster that we’ve feared. First, a summary of where the hurricane stands now:

THE EYE OF IRENE MOVED OVER ABACO ISLAND EARLIER THIS AFTERNOON. AN AUTOMATED WEATHER STATION ON THE ISLAND MEASURED A MINIMUM PRESSURE OF 950.4 MB AROUND 1700 UTC. THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING IRENE THIS AFTERNOON HAS REPORTED A 700 MB PEAK-FLIGHT WIND OF 99 KT [114 MPH]. ALTHOUGH RECENT AIRCRAFT DATA DO NOT QUITE SUPPORT THE 100-KT [115 MPH] ADVISORY INTENSITY…WE WILL HOLD THE INTENSITY FOR A LITTLE LONGER TO SEE IF THE AIRCRAFT FINDS HIGHER WINDS.

Okay, some translation is needed from geek-speak. It may sound like the NHC is simply quibbling over whether the winds are 114 mph or 115 mph, but that’s not the case. The recon aircraft found a peak flight-level wind of 114 mph. Normally, that translates to something in the ballpark of 100 mph at the surface. (Winds are stronger aloft.) So, in other words, if the NHC was relying strictly on this data, Irene would be classified as a borderline Cat. 1/2 hurricane, with winds somewhere around 100 mph, not a Category 3 with winds of 115 mph.

The central pressure of 950mb is awfully low for a borderline Cat. 1/2 storm — but then, that sometimes happens in very large, sprawling hurricanes, which Irene is. Realistically, Irene has probably been no stronger than Category 2 ever since last night, when it started, or attempted to start, an eyewall replacement cycle. (The 11am advisory suggested that it was unclear if the cycle had actually completed. Irene may be stuck in some sort of eyewall replacement limbo. Unfortunately, those dynamics are very poorly understood, even by the best meteorologists on the planet. Hurricanes are complex and, in many ways, still very mysterious beasts.)

So why is Irene still classified as a Category 3, with 115 mph winds, if it’s an open secret that she’s actually weaker than that? Because the Hurricane Center is very, very cautious about officially downgrading land-threatening hurricanes that it expects to re-strengthen. Frankly, there’s some art as well as science in the sustained-wind estimation process, and the NHC is wont to take a little bit of artistic license at times like these — for understandable reasons. Forecasters don’t want people to “let their guard down,” falsely thinking that a temporarily-weakened storm is no longer a big deal. So they will maintain a storm like Irene at a higher intensity than its likely “true” strength for some period of time, waiting for the expected restrengthening. Eventually, though, the NHC has to bow to the data, and the 5pm advisory is telegraphing that Irene is likely to be downgraded to a Category 2 if it doesn’t get its act together soon.

That brings us to the next encouraging part of the discussion — the forward-looking intensity discussion:

THERE IS STILL SOME TIME FOR IRENE TO STRENGTHEN AS IT WILL BE MOVING OVER WARM WATER AND THE SHEAR REMAINS LOW. HOWEVER…THE UPDATED FORECAST CALLS FOR A LITTLE LOWER INTENSITY OVER THE FIRST 24-36 HOURS. IN ABOUT 48 HOURS…SOUTHWESTERLY SHEAR IS FORECAST TO INCREASE…WHICH SHOULD START A WEAKENING PROCESS. HOWEVER…SINCE IRENE HAS SUCH A LARGE AND INTENSE CIRCULATION…IT WILL PROBABLY BE SLOW TO WEAKEN.

The previous advisory called for Irene to peak at 125 mph, and stay above 120 mph for 24-36 hours. (The amount of time she’s a major hurricane is important, because it means a lot more huge surf and storm surge builds up ahead of the storm, which eventually gets pushed ashore somewhere.) This advisory, by contrast, calls for Irene to peak at 120mph, and to maintain that intensity for just 12 hours, give or take. So she’d be a little less strong, and stay that way for a little less long.

Now, because intensity forecasting is so inexact, it may sound a little silly to obsess over such relatively small variations. But — stop me if you’ve heard this one before — the trend is your friend. And the trend is clearly indicating that the NHC is losing confidence that Hurricane Irene will substantially re-strengthen before shear, cold water, and perhaps land interaction with the Carolinas begin to induce weakening.

Keep in mind, Irene is “really” probably a ~100mph hurricane right now, so strengthening to 120mph (which is what is officially being forecast) would be fairly substantial. If that happens, it would indicate she’s gotten her act back together, and it’s quite possible she might get a good bit stronger still, after all. On the other hand, it’s very conceivable that she might never make it back to “true” Category 3 (115+) status (notwithstanding that she’s officially a Cat. 3 — a “Major Hurricane In Name Only,” or MHINO, for you political types — right now).

Either way, the odds of Irene becoming a monster high-end Cat. 3 or low-end Cat. 4 as she menaces the Carolinas, then weakening only to Category 2 strength before hitting the northeast, have decreased (although that scenario is still possible). Conversely, the odds of Irene hitting North Carolina as a Cat. 2, the mid-Atlantic as a Cat. 1, and New York/New England as a minimal hurricane or high-end tropical storm, or something along those lines, have improved.

Now, again, for the enormous caveat. This does not mean anyone can breathe easy. It is still very possible that Irene could become the monster we’ve all been fearing. The meta-conditions are ripe for it to happen; the jet stream, which can cause a hurricane to explode like jet fuel poured on a fire, is dead ahead; intensification could happen, and happen rapidly. The only question is whether the poorly understood internal dynamics of Irene’s eyewall and core structure will permit it. WE JUST DO NOT KNOW the answer to that question. It could go either way.

Moreover, even if Irene doesn’t become a monster, she’ll do plenty of damage, ESPECIALLY in terms of inland flooding, which may very well end up causing the most damage to life and property. But the wind and surge could be pretty bad too, given the vulnerability of the targeted areas.

So, please, please, if you’re in a potentially affected area, DO NOT GROW COMPLACENT and DO NOT STOP PREPARING FOR THE WORST. Things could still be very bad. But there’s a bit more hope than there was 90 minutes ago.

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Remember the famously apocalyptic National Weather Service statement ahead of Hurricane Katrina, predicting “human suffering incredible by modern standards”? Well, this statement by the Hydrometeorological Prediction Center isn’t quite that dire, but…

THE LATEST NUMERICAL GUIDANCE CONTINUES TO ADJUST WESTWARD AS HAS THE LAST SEVERAL NHC TRACK FORECASTS WHICH NOW HAVE EYE OF IRENE COMING THRU THE NORTH CAROLINA OUTER BANKS LATE SATURDAY BEFORE GRAZING THE DELMARVA AND NEW JERSEY THEN MOVING INTO THE NORTHEAST ON SUNDAY. THIS POTENTIALLY COULD BE EXTREMELY DESTRUCTIVE WITH MASSIVE DISRUPTIONS TO SOCIETY AND COMMERCE ALONG ITS ENTIRE TRACK WITH VERY HIGH WINDS/STORM SURGE/OCEAN OVERWASH/BEACH EROSION/SOUND AND BAY SIDE COASTAL FLOODING AND EXTREME TIDE POTENTIAL. WIDESPREAD HEAVY RAINS IN THE 6-10 INCH RANGE WILL BE COMMON WITH GREATLY INCREASED INLAND FLOOD POTENTIAL.

Yup.

Again, my Twitter feed has much more.

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