Get PJ Media on your Apple

Weather Nerd

Monthly Archives: October 2008

Quiet in the tropics

October 27th, 2008 - 6:49 am

Dr. Jeff Masters wrote on Saturday:

The tropical Atlantic remains quiet today. There are no threat areas to discuss, and none of our reliable models are calling for tropical storm formation over the next seven days. The next area to watch is the Western and Southern Caribbean beginning on Wednesday, when a cold front will stall out over the area and potentially act as a nucleus around which a tropical storm could form. This should give time for flooding to subside in Honduras, where 29 are dead and 14 missing due to recent rains.

Although that post was written two days ago, there’s nothing new to report. The tropics remain very quiet, even moreso than you’d expect for this time of year (though the season is winding down, climatologically). That’s partly due to the premature winter pattern, which I’ve mentioned several times before, and which Alan Sullivan refers to today as Christmas at Halloween.

Deadly flooding strikes Central America

October 21st, 2008 - 9:33 am

Even as an early winter pattern largely shuts down the Atlantic hurricane season, with little threat of further hurricane activity in the U.S., areas closer to the equator remain at risk of death and destruction, including from weak, nameless systems. Take Tropical Depression 16 and “Invest 91L,” which have combined to reak havoc on Central America with their heavy rains:

A week of heavy rains over northern Honduras, northern Guatemala, and Belize due to Tropical Depression Sixteen and a Western Caribbean tropical disturbance (91L) have resulted in record flooding and deadly mudslides across the region. In Honduras, a nationwide state of emergency has been declared, and at least eleven people are dead and two missing from the flooding. Two large landslides blocked the Coyol River in western Honduras yesterday, forming a lake 500 feet deep. Engineers are attempting to drain the lake today, but they won’t be helped by the weather–91L promises to move little the next two days, and will continue to dump heavy rains on the region. In Belize, damage is already estimated in the ten of millions, and some areas are seeing flooding worse than was experienced during Hurricanes Mitch and Keith. In northern Guatemala, at least 70 towns have been cut off by flood waters and a state of emergency has been declared. Satellite estimates suggest up to a foot of rain has fallen over the region in the past week.

That write-up is from Dr. Jeff Masters, who adds (and the NHC concurs) that “91L” is very unlikely to develop — it’s too close to land, and wind shear is too high. But that hardly matters to the people in the affected regions. Even a nameless, undesignated tropical disturbance can cause massive destruction in vulnerable areas, and this one is doing just that.

Eventually, 91L will move away from Central America and head toward Florida, though by then its tropical potential should be gone entirely:

A trough of low pressure swinging across the Midwest U.S. should be able to start pulling 91L northward or northwestward by Thursday. Once 91L enters the Gulf of Mexico on Thursday, the trough should swing the storm to the northeast, bringing it across the west coast of Florida between Tampa and the Big Bend region on Friday night. Wind shear will be very high over the Gulf of Mexico this week, in the 30-40 knot range, and 91L is expected to make a transition to a very wet extratropical storm by Friday. The storm should bring sustained winds of 30-35 mph and heavy rains of 2-3 inches to Florida.

In other news, a Houston Chronicle report out today reveals that Hurricane Ike damaged more than half of Houston’s 2,000 apartment complexes. The Chronicle also has a section on its website devoted to Ike’s missing.

Finally, on an almost entirely unrelated note, check out these amazing photos and videos of the Sun, courtesy of the Boston Globe‘s excellent “The Big Picture” blog. (Hat tip: Eric Berger.)

Omarrr causes little damage

October 17th, 2008 - 7:52 am

[UPDATE: This report by Dr. Jeff Masters suggests there was somewhat more damage that I thought when I first published this post. The damage was caused in part by Omar's "unusual west-to-east motion [which] resulted in storm surge and waves affecting the western side of the islands, which are not as well-defended against these effects.” Read the whole thing.]

*   *   *   *   *

First off, no, the title of this post isn’t a typo. I just couldn’t resist calling Hurricane Omar “Omarrr,” in light of the fact that “Ol’ Chumbucket” — one of the “Pirate Guys” who created International Talk Like a Pirate Day — filed several video reports on Omar from St. Croix. Arrr!

(It should be noted that Chumbucket & family were in Frederiksted, on the west end of the island, so they would have experienced far less severe conditions than those on the east end, where the eyewall hit.)

On a more serious note, Dr. Jeff Masters writes this morning that Omar caused mostly minor damage across the affected islands:

Thankfully, no deaths or injuries have been reported from the storm, which avoided making a direct hit on any islands. Hardest hit appears to be the island of Antigua, where 5.71″ of rain was recorded at the airport. Severe flooding washed out roads and prompted many boat rescues, putting up to 100 people in shelters. St. Croix, whose eastern tip caught the eyewall winds of Omar, received minor damage, according to media reports. The storm did knock out power to the entire island for nearly a day, and caused considerable damage to piers and boats in the main harbor, though. Flooding was also reported in the British Virgin Islands, St. Martin, and St. Kitts and Nevis. On St. Martin, high waves dumped rocks and sand of the runway of the airport, forcing its closure. The airport was scheduled to be reopened today.

As Masters notes, stormcarib.com has more details on Omar’s impact.

Masters also writes this:

Several computer models are predicting the development of a tropical depression in the Atlantic’s southwestern Caribbean, off the coast of Nicaragua or Honduras, about 5-8 days from now. Wind shear is expected to be low, 5-10 knots, across most of the Caribbean for the next ten days, and I would not be surprised to see a tropical storm develop in the Caribbean next week.

A hypothetical proto-Paloma? (Hypo-Paloma?) We shall see.

Hurricane Omar peaked overnight at 959 millibars and 130 mph sustained winds, making it a borderline Cat. 3/4 hurricane, but it took a “best-case scenario” track through the narrow Anegada Passage between the Virgin Islands to the west and St. Maarten and Anguilla to the east.

A few miles further west, and Omar would have made a direct hit on St. Croix, instead of delivering a glancing blow there. A few miles further east, and the impact on St. Maarten and Anguilla would have been quite severe. Instead, the storm “threaded the needle,” as Alan Sullivan put it yesterday, and spared everyone the worst. Sullivan, who has a friend living on a boat in St. Maarten, is understandably relieved.

Dr. Jeff Masters notes that St. Croix did experience hurricane-force winds, but Omar certainly will not have been the disaster that was possible if it had taken a slightly different track. Such are the unpredicable vagaries of these intense but fickle beasts we call hurricanes.

Now, Omar is quickly weakening as it moves out to sea, with maximum sustained winds down to 85 mph and dropping, inspiring the National Hurricane Center forecasters to opine in the 11am EDT discussion:

IT IS SIMPLY AMAZING TO ME AT HOW QUICKLY A HURRICANE CAN SPIN UP AND JUST AS QUICKLY FALL APART. OMAR REACHED NEAR THE THRESHOLD OF CATEGORY 4 EARLY THIS MORNING AROUND [2:00 AM] AND NOW WE HAVE AN EXPOSED LOW-LEVEL CENTER SHOWING UP IN THE VISIBLE SATELLITE IMAGERY JUST A FEW HOURS LATER.

Omar is expected to continue weakening over open water, eventually becoming extratropical as it heads toward the far distant Azores.

Meanwhile, Tropical Depression 16 has dissipated over Hondruas (there’s your unnamed T.D. for the season, Chris). Its remnants could potentially regenerate over the Eastern Pacific, which means that “proto-Paloma” is now “proto-Polo.” (Too bad “Marco” and “Polo” weren’t active at the same time. They could have shouted at each other, over Central America: “Marco!” “Polo!” Heh.)

With the demise of T.D. 16 and the decline of Omar, Sullivan thinks we’re done: “That should do it for the 2008 hurricane season,” he writes. Perhaps so, but if it sounds like you’ve heard that one before, well, you have: three weeks ago, Sullivan wrote, “with polar influences expanding so swiftly, there may never be a Kyle at this rate”; then, six days later, after the birth and death of Kyle and Laura, I wrote, “With an early winter pattern developing, there may never be a Marco.” Heh.

Since my brilliant prognostication, we’ve seen Marco, Nana and Omar — though Sullivan regards some of these late-season “designations” as “marginal,” specifically Laura and Nana, if I’m not mistaken. Along these same lines, commenter Steve Sadlov wrote this morning on Sullivan’s site, “Omar was not Omar, it was Marco.” I’m going to vote “present” on this particular “count-padding” question, but I’ll just add that, if we’re going to discount Laura and Nana, maybe we should add in the subtropical-ish system that hit the Carolinas in late September. In hindsight, maybe that was the true “Laura,” in which case Marco was still Marco, and Omar should have been Nana, no?

In any event, the hurricane season officially continues for another month-and-a-half, so I’ll hold off on declaring it “over” just yet. But at least in the short-term, according to Dr. Masters, things are likely to remain quiet: “No computer models are forecasting tropical cyclone development in the Atlantic over the next seven days.”

Omar becomes a major hurricane near islands

October 15th, 2008 - 9:29 pm

Hurricane Omar strengthened to a Category 3 storm tonight as it swiped St. Croix, the southernmost of the Virgin Islands, and moved toward the Anegada Passage in between the Virgin Islands and the northern Antilles islands of Anguilla and Saint Maarten.

Here’s the 11:46 PM EDT radar view from San Juan:

Here’s a wider radar loop.

Omar’s winds are currently estimated at 115 mph, and that “COULD BE CONSERVATIVE,” according to the National Hurricane Center’s 11:00 PM EDT discussion. Further strengthening is possible overnight.

The big question mark is Omar’s exact track. The current official forecast predicts that the storm will “thread the needle,” as Alan Sullivan put it hopefully earlier today, between the Virgin Islands and the northern Antilles. This is helpfully shown by the guiWeather Google Map layer:

However, as the NHC discussion notes, “THE MODEL GUIDANCE KEEPS FORECASTING A 15-20 DEGREE LEFT TURN THAT SO FAR HAS NOT OCCURRED.” If that turn doesn’t occur, or is delayed further, Anguilla and/or St. Maarten could take a direct hit from Omar’s eyewall. Sullivan is worried, writing at 11:53 PM EDT: “St. Maarten needs a northward, leftward wobble soon, or the worst part of the storm, the southern eyewall, may hit the island when the storm is peaking in strength.”

Here’s a look at Omar’s path so far, along with its wind field (tropical storm force winds in orange, hurricane force in maroon) and its accompanying watches and warnings (red for hurricane warnings, pink for hurricane watches, blue for tropical storm warnings, yellow for tropical storm watches):

StormCarib has coverage.

Tropical Storm Omar became a hurricane at 11:00 PM EDT last night, and at that time, it appeared likely to continue strengthening overnight. But wind shear disrupted the storm somewhat this morning, slowing its intensification. If not for the shear, we could be looking at a Category 2 or even 3 hurricane by now.

Now, however, as of 11:00 AM EDT, it appears Hurricane Omar is strengthening again. Top sustained winds are up to 85 mph, and are forecast to reach 105 mph — enough for Category 2 status — as the storm passes through the Virgin Islands tomorrow morning.

Omar is actually expected to make its initial landfall (or near-landfall) at St. Croix very late tonight or very early tomorrow — around midnight, give or take a few hours — and then continue northeastward toward the rest of the Virgin Islands. It will be exiting the islands by around 8:00 AM EDT, which is when the NHC forecast calls for 105 mph winds.

Here’s what the NHC’s 11am discussion says about the potential for further strengthening:

NOW THAT A DISTINCT EYE AND EYEWALL HAVE DEVELOPED…A GOOD CHIMNEY EFFECT CAN BE ESTABLISHED AND OMAR COULD GO THROUGH A BRIEF PERIOD OF RAPID INTENSIFICATION AGAIN.  ONLY THE GFDL MODEL IS CALLING FOR OMAR TO STRENGTHEN TO AT LEAST 90 KT.  THE REMAINDER OF THE INTENSITY GUIDANCE HOLDS OMAR BELOW 80 KT.  BASED ON THE BETTER DEFINED EYE FEATURE…AND THE FACT THAT OMAR IS A RELATIVELY LOW SHEAR ENVIRONMENT AND OVER 29C AND WARMER SSTS…ADDITIONAL INTENSIFICATION SIMILAR TO THE GFDL MODEL SEEMS QUITE REASONABLE.  IT ALSO ISN’T OUT OF THE QUESTION THAT OMAR COULD ACHIEVE MAJOR HURRICANE STATUS JUST BEFORE THE CYCLONE REACHES THE NORTHERN LEEWARD ISLANDS.  HOWEVER…THE RAPID ENCROACHMENT OF DRY MID-LEVEL AIR FROM THE NORTHWEST AS NOTED IN WATER VAPOR SATELLITE IMAGERY PRECLUDES EXPLICITLY FORECASTING THAT INTENSITY AT THIS TIME SINCE THAT DRY AIR COULD MAKE IT INTO THE INNER CORE REGION IN 12-18 HOURS AND WEAKEN THE HURRICANE.

Dr. Jeff Masters, in a post published shortly before the 11am advisory came out, writes:

The models are tightly clustered along a path that would take Omar through the Virgin Islands late tonight. However, the east coast of Puerto Rico and the islands farther east, such as St. Martin/St. Maartin and Anguilla, are still in the cone of uncertainty, and could get a direct hit. Our main intensity models–the GFDL, HWRF, and SHIPS–all forecast that Omar will be a Category 1 hurricane with winds of 75-85 mph as it passes through the islands. Wind shear is expected to be in the moderate to high range, 15-25 knots, over the next two days, which should allow some modest intensification. I give Omar a 30% chance of reaching Category 2 strength before landfall early Thursday morning, and a 10% chance of being a major Category 3 hurricane.

You can follow the storm’s progress on long-range San Juan radar.

Meanwhile, it now appears less likely that Tropical Depression 16 will become Tropical Storm Paloma. The system’s ill-defined center has moved ashore, or nearly so, in Honduras. There is still a chance it could become a minimal tropical storm as it meanders westward, but that is mostly a technicality. This will be a rain-maker but nothing more.

At 11:00 AM EDT, Tropical Depression 15 in the Eastern Caribbean became Tropical Storm Omar, and “Invest 99L” in the Western Caribbean became Tropical Depression 16. Both Omar and “proto-Paloma” are expected to strengthen.

Omar, in fact, “MAY BE STARTING A PERIOD OF RAPID STRENGTHENING,” according to the National Hurricane Center discussion. The official forecast calls for Omar to reach hurricane status at roughly the same time as it’s passing over the Virgin Islands. (The track has shifted east, away from Puerto Rico, and may shift further east if the computer models hold.)

Dr. Jeff Masters writes:

The storm is expected to drift southeastward until an upper-level trough of low pressure swings far enough south tonight to pull the storm northeastward towards Puerto Rico, the Virgin Islands, and the northern Lesser Antilles Islands. Variations in timings between the models have narrowed some, with landfall in the Virgin Islands, northern Lesser Antilles Islands, or eastern Puerto Rico expected sometime between Wednesday afternoon and Wednesday night. Heavy rains should spread into the islands tonight, generating additional rainfall totals of 5-10 inches. The eastern portion of the Dominican Republic will likely get 3-6 inches, and Haiti will escape heavy rains from the storm.

T.D. Sixteen, meanwhile, is expected to become Tropical Storm Paloma today or tomorrow. However, the intensity forecast is very uncertain because a great deal depends on the depression’s track. If the center stays just north of Honduras, as currently expected, strengthening is likely. In Dr. Masters’s words: “As long as the center remains over water more than 50 miles from land and does not stall out, intensification should occur.” But a slight deviation to the south would move T.D. 16 over land, and cut off the opportunity for intensification.

And deviations from the forecast are very possible. As Eric Berger notes, Sixteen “is quite interesting because the steering currents aren’t all that strong.” Some models even “bring the system into the Pacific Ocean and develop it there into a tropical storm.” So it’s anybody’s guess right now, though the most likely scenario is that proto-Paloma goes “north, then west into Belize.”

Masters writes:

The system will likely bring 5-10 inches of rain to northern Honduras today through Thursday, potentially causing flash flooding and destructive mudslides. Rain amounts of 2-4 inches are likely today over northeastern Nicaragua and the Cayman Islands. Heavy rains of 4-8 inches will likely affect Belize, northeastern Guatemala, and portions of Mexico’s Yucatan Peninsula tonight through Wednesday night. The heaviest rains will stay south of the resort areas of Cancun and Cozumel, though.

It currently appears that the center of 99L will stay close enough to the coast that the storm will not grow large and strong enough to tap into the Pacific Ocean as a major source of moisture. However, the counterclockwise flow of air around the storm is already strong enough that it is pulling in air from the Pacific over northern Costa Rica and Nicaragua. This moist flow of air should generate rain amounts of 2-4 inches today along the Pacific coasts of these countries. If 99L were to grow into a strong tropical storm, this moist flow of air would be capable of generating very dangerous rains in the 10-15 inch range along the Pacific coast of Central America.

Nana dissipates; no Omar yet

October 14th, 2008 - 5:05 am

Sometimes the National Hurricane Center forecasters get punchy in the wee hours of the morning:

NANA HASN’T BEEN PRODUCING ENOUGH CONVECTION TO QUALIFY FOR TROPICAL CYCLONE STATUS FOR MANY HOURS…SO IT’S TIME TO SING NA NA HEY HEY KISS HER GOODBYE.

Heh.

Meanwhile T.D. 15 is still threatening to become Omar, but hasn’t managed it yet. Tropical Storm Watches are up for Puerto Rico and environs.

And in the Western Caribbean, Invest 99L could become T.D. 16 today. Alan Sullivan is concerned about it:

TD #15 is a huge rainmaker, destined to move NE as a tropical storm, deluge the Virgin and Leeward Islands, then head out into the North Atlantic. [99L] could be even more troublesome. I see marked similarities to the formative stages of deadly Mitch in 1998. It seems likely that I will be making hurricane updates for some time.

Three depressions?

October 13th, 2008 - 9:15 am

As expected, Tropical Storm Nana has weakened to a depression. Meanwhile, “Invest 98L” in the Eastern Caribbean has been designated Tropical Depression 15. And now there’s a new disturbance, “99L,” in the Western Caribbean, which spurred a Special Tropical Disturbance Statement at 11:30 AM EDT, and which could potentially become T.D. 16 “during the next couple of days.”

If either Fifteen or proto-Sixteen earns a name, it would be Omar, the first time that name has ever been used. The current list in the sexennial storm-name rotation has been used five times: in 1984, 1990, 1996, 2002 and 2008. Three of those seasons (’90, ’96 and ’08) have produced a “Marco,” and two (’90 and ’08) have produced a “Nana,” but we’ve never reached “Omar” — still less “Paloma,” which is next on the list. This fact is of no particular significance, but sometimes I like to geek out about storm-name history.

Anyway… the biggest concern right now is T.D. 15, which is expected to track northeastward toward Puerto Rico, and which could — could — become a hurricane. But the intensity forecast is uncertain, and Dr. Jeff Masters is skeptical that Fifteen will get its act together quite so quickly:

Wind shear is expected to fall to the moderate 10-20 knot range over the next three days, and waters will remain warm, 29°C. This should allow [TD 15] to intensify into a tropical storm by Tuesday. The HWRF and GFDL models both intensify TD 15 into a hurricane before it hits Puerto Rico on Wednesday. This seems overly aggressive, given the moderate 10-20 knots of wind shear expected. The SHIPS model forecast and official NHC forecast of a strong tropical storm hitting the island on Wednesday is more reasonable.

Regardless of its intensity, the main threat from T.D. 15 will be heavy rain:

Up to five inches of rain has already fallen over the Virgin Islands and eastern Puerto Rico, and additional heavy rains of 5-10 inches are likely over these islands through tonight. Heavy rains of 5-10 inches per day will likely spread to the eastern Dominican Republic and the northern Lesser Antilles Islands by Tuesday morning, and continue through Wednesday night. Over Puerto Rico, isolated rain amounts in excess of 20 inches are possible before the storm clears the islands by Thursday.

Thankfully, “it currently appears that Haiti will only get 1-3 inches of rain from TD 15.” Haiti has already suffered more than its share of misery this hurricane season, mostly due to flooding from torrential rains.

The National Hurricane Center designated a disturbance in the Eastern Atlantic as Tropical Storm Nana Sunday afternoon — and immediately announced its imminent demise:

THE LONG-TERM SURVIVAL OF NANA SEEMS BLEAK AS STRONG UPPER-LEVEL WESTERLIES ARE FORECAST TO CONTINUE. ALL THE INTENSITY GUIDANCE SHOWS WEAKENING AND SO DOES THE OFFICIAL FORECAST. THE OFFICIAL FORECAST SHOWS NANA DEGENERATING INTO A REMNANT LOW IN ABOUT 48 HOURS…BUT IT WOULD NOT BE SURPRISING IF IT OCCURRED SOONER.

Alan Sullivan mocks the NHC’s decision as an example of count-padding. Whether he’s right about that is above my pay grade, but regardless, Nana is expected to weaken to a tropical depression or even a remnant low on Monday.

Meanwhile, Sullivan wonders whether the NHC will similarly designate the sheared disturbance in the Eastern Caribbean — currently “Invest 98L” — as Tropical Storm Omar tomorrow. Perhaps so; the Tropical Weather Outlook gives 98L a better than 50% chance of becoming a tropical depression in the next 48 hours.

Dr. Jeff Masters has a full update on both storms, albeit written Sunday afternoon when Nana was still “97L.”