Harvey drenching Belize; 97L a threat to the Caribbean and U.S.

By: Dr. Jeff Masters , 4:16 PM GMT on August 20, 2011

Tropical Storm Harvey is closing in towards a landfall this afternoon in Belize, and is dumping very heavy rains on northern Honduras, northern Guatemala, and Belize as it steadily moves west near 12 mph. A personal weather station on Roatan Island on the north coast of Honduras has received 6.68" of rain as of 10am EDT this morning from Harvey, and had a peak wind gust of 42 mph. The Roatan airport has received 3.55", and had a peak wind gust of 40 mph. The first significant spiral band from Harvey moved over Belize City at 7am local time, dropping nearly an inch of rain on the city. Belize National Meteorological Service radar shows that Harvey has appeared to close off an eyewall as of 11:30am EDT, which may allow the storm to intensify another 10 - 15 mph before landfall. The 11am NHC wind probability forecast gave Harvey a 3% chance of making it to hurricane strength, but the discussion noted that it wouldn't be that hard for Harvey to gain another 10 - 15 mph before landfall. I estimate there is a 30% chance that the winds along a 10-mile stretch of Belize coast where the eyewall makes landfall will reach hurricane force.


Figure 1. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.


Figure 2. True-color MODIS image of Tropical Storm Harvey taken at 12:25pm EDT on Friday, August 19, 2011. An hour after this picture was taken, Harvey became a tropical storm with 40 mph winds. Image credit: NASA.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Harvey is the 8th named storm this year, and its formation date of August 19 marks the 4th earliest date on record for the Atlantic's 8th storm. Only 2005, 1933, and 1936 had the 8th storm of the season form earlier. All eight storms this year have stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in yesterday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. With 97L looking like it will become a named storm in the next few days, at our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, we are using the 2005 list of names this year, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing a hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 3. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Invest 97L likely to become a tropical storm by Tuesday, could threaten the U.S.
A tropical wave near 14°N 56°W, about 450 miles east of the Lesser Antilles Islands, is moving west to west-northwest at 15 - 20 mph. This wave, designated Invest 97L, has built a respectable amount of heavy thunderstorm activity over the past day, but remains disorganized. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. An impressive amount of large-scale spin is obvious in visible satellite loops, but there is no sign of a well-defined surface circulation. An ASCAT pass at 9:04am EDT this morning showed a strong wind shift, but no closed circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm. A hurricane hunter aircraft will investigate 97L this afternoon.


Figure 4. Morning satellite image of the tropical disturbance Invest 97L.

The computer models have shifted southwards since yesterday, and now take 97L south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, 97L should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. We can expect that 97L will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether 97L's turn to the north will take the storm into the Gulf of Mexico or not.

The computer models continue to enthusiastically develop 97L, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.

There has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties. There will be some moderate wind shear of 10 - 20 knots to the north of 97L over the next week, and this shear may work in concert with the dry air to slow development.

Given 97L's current disorganization and problems with dry air, I believe it is unlikely the storm will be stronger than a 55 mph tropical storm on Tuesday morning, when it will be close enough to the mountainous island of Hispaniola that a good portion of its circulation will be over the island, disrupting the storm. 97L may also make a direct hit on the Dominican Republic or Haiti sometime Tuesday or Wednesday morning, which could even destroy the storm, like happened to Tropical Storm Emily in early August. However, there is at least a 30% chance that 97L will miss Hispaniola, and slide through the waters between Jamaica and Eastern Cuba, allowing the storm to intensify into a hurricane south of Cuba. At this point, it appears there are too many hurdles for 97L to negotiate for it to arrive in the Florida Straits as a hurricane, since the storm has to cross Cuba and/or Hispaniola, plus contend with dry air and wind shear. However, 97L hasn't even developed a well-defined circulation yet, making it difficult for the models to zero in on a solution for where the storm might go. The average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles; the error will be much higher for a 6 to 7-day forecast of an Invest that hasn't developed yet. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or Florida, since 97L could well be paying you a visit as a tropical storm or hurricane sometime in the next week.


Figure 5. Skill of computer model forecasts of Atlantic named storms during 2010. OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; NOGAPS=Navy Operational Global Prediction System model; UKMET=United Kingdom Met Office model; ECMWF=European Center for Medium Range Weather Forecasting model; TVCN=one of the consensus models that lends together all (or most) of the above models. Image credit: National Hurricane Center 2010 verification report.

Which model should you trust?
Wunderground provides a web page with computer model forecasts for many of the best-performing models used to predict hurricane tracks. So which is the best? Well, the best forecasts are made by combining the forecasts from three or more models into a "consensus" forecast. Over the past decade, NHC has greatly improved their forecasts by relying on consensus forecast models made using various combinations of the GFS, GFDL, NOGAPS, UKMET, HWRF, and ECMWF models. If you average together the track forecasts from these models, the NHC official forecast will rarely depart much from it, and the NHC forecast has been hard to beat over the past few years. The single best-performing model over the past two years has been the ECMWF (European Center model). This model out-performed the official NHC forecast in 2010 for 1-day, 2-day, 3-day and 4-day forecasts, and in 2009 for 4-day and 5-day forecasts. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models. As seen in Figure 5, over the past two years, the GFS and GFDL model have been the next best models, with the UKMET model not far behind. Last year, the NOGAPS model did very poorly, forcing NHC to come up with some new consensus models this year, the TCOA and TVCA, that do not include the NOGAPS model. For those interested in learning more about the models, NOAA has a great training video (updated for 2011.)

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today before running into more hostile conditions on Sunday. NHC gave the storm a 40% chance of developing into a tropical depression by Monday morning in their 8am advisory. Once 98L passes to the east of the Lesser Antilles, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Dismal Swamp fire creating dangerous air pollution in Virginia
Lightning from a thunderstorm on August 4 sparked a fire in Southeast Virginia's Dismal Swamp, which continues to burn out of control. Yesterday, air quality alerts for Code Purple pollution--the worst category of air pollution--were posted for Suffolk, Virginia and continue today. The region, including the cities of Norfolk and Hampton Roads, have seen an increase in hospital admissions for people with breathing problems, plus an increase in traffic accidents due to low visibility conditions on area roads. The fire has burned 6100 acres and is 15% contained. Given that it is burning more than 1 foot underground, it will be difficult to put out unless heavy rains raise the water table. The region is under "Abnormally dry" drought conditions, the lowest category of drought on the five-category drought scale.

Jeff Masters

Tropical Storm Harvey (mchavez)
Raining @ Roatan Bay Islands
Tropical Storm Harvey

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Quoting Bluestorm5:
of course, Irene is #1 and #2...


According to this 1936 season archive, although their #9 is listed as having formed on the 20th, it says something to the effect of... by 7pm EST no low level center could be located...

granted it was 1936, but their specificity technically gives Irene sole possession of #2 by at least a few hours.

Link
(page 6)
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Quoting HCW:
TWC just said that it's not even a depression yet

*facepalm*
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2384. hotrods
So many maps, so many model runs, tracks to the right,tracks to the left, tracks up the middle-- "places a map on the wall, takes 10 steps back throws a dart, ok that track looks good to me" !
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Wow...97L looks to be taking off actually in that NE storm cluster...which is looking increasinly like a CDO...I think 97L is consolidating to the NE....

http://www.ssd.noaa.gov/goes/flt/t2/avn-l.jpg

I'd give this now a 100% chance of tropical cyclone formation in the next 48 hours...
Member Since: December 31, 1969 Posts: Comments:
Quoting Clearwater1:
Not a troll, just asking for you to verify. Geezz. Where is the discussion concerning "Irene". Is that too much to ask without being insulted.
Irene's been renumbered at the Navy website. NHC has to do all the other preps for public consumption, including notification of all the WX stations in the Leewards, posting of watches, etc. They'll likely post to their website within the next hour.
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2381. ncstorm
Quoting HCW:
TWC just said that it's not even a depression yet


good gosh..what a joke!
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Quoting HCW:
TWC just said that it's not even a depression yet




lol they dont look at recon data
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2379. HCW
Sad thing is that TWC just said they talked to the Hurricane hunters
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18z hwrf 42 hours out
Member Since: December 31, 1969 Posts: Comments:
Part of the delay at this point is the time it takes the NHC to sort out all the various watch/warnings to be issued by various island governments, before an advisory can be issued.
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Quoting MiamiHurricanes09:
West coast would mean bad news for the east coast since the strongest winds are located in the eastern quadrant...if that makes any sense lol. And of course, east coast would mean bad news for the Bahamas. Obviously if it were to intensify into a pretty potent hurricane, then regardless of east/west coast, all of Florida is gonna be in for a rough ride.
Yeah that's true we may have a Hurricane this time to deal with, unlike with Fay & Ernesto, so both sides of the state would be in for a rough ride, especially considering FL. is pretty flat and so even if it splits the middle it will be going up the Everglades which is no different than being over the water.
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I just heard on the weather channel that it is not a tropical depression yet...that the hurricane hunters said that it will be soon though...
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gilbert like conditions for jamaica? or will it be north cloudburst?
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2372. Levi32
Quoting weatherjr:
Levi32: Is Irene moving WNW or W-WNW? I mean it will pass closer to PR than models consider? Just your opinion. I think it will move closer to PR (or over PR).


It's probably close to a true WNW heading right now, but hard to tell as long as the center is not easily-discernible on satellite, and now we're losing the visible daylight so it will be even harder.
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2370. HCW
TWC just said that it's not even a depression yet
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Quoting CaribBoy:


The local weather service said we should experience gusts over 60MPH all day sunday here in the northern leewards (st martin)


PR should be preparing for a storng TS or a cat 1 cane in a rush!
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I really see no way that the center can stay as far south as it is now. Pretty intense convection continues to burst NE of the surface circulation...it is bound to relocate more to the north and east with time unless something can get going over the center.

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so we now have Irene?? Geez why is it the "I"s that bring the nice suprise punch? Looks like it might stay on that w wnw course though..and that's not good at all...the water temps are WAY too hot...she's going to be taken a very hot bath here soon i believe..
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Quoting CosmicEvents:
I think it was a TS....but it did cause lots and lots of flooding.
not even close got a strong cv system now
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Never mind, must have been a glitch, fixed now.
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Quoting CosmicEvents:
I think it was a TS....but it did cause lots and lots of flooding.
I remember Irene in 1999 too. My first Hurricane (I think it was briefly a mild Cat 1) and I thought, "whats the big deal"? Then I met Wilma and have NEVER asked that again!!
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Quoting dfwstormwatch:

36 hours out




from 997 too 993 too 989 too 986 too 976mb


ouch
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Quoting Tazmanian:



from 997 too 993 too 989 too 986mb


ouch wow eeeeeeeeeeek


falling fast huh. That can't be good
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Quoting stormpetrol:
I don't care if I get called a westcaster/wishcaster, but Irene might take a similar track to Harvey only a bit further north.
I don't think that southern route is as likely as it was yesterday. The storm's already far enough north, and unlike Harvey, it'll be strong enough to feel that gaping weakness. Maybe we'll see a track south of the big islands, but I doubt south of JA....
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Quoting dfwstormwatch:

36 hours out

*GULP*
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Quoting Chucktown:


The northwest solution after landfall that the 18 Z GFS is showing is a possiblity. Once that weakness "closes" by next weekend, the storm may not have a chance to escape northeast. I said this last week, this could be a Fay type set up - weak steering and slow movement by this time next week.
Only difference this time is that it might make a run at Hurricane strength.
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36 hours out
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2356. Patrap
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192hrs.

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Quoting GTcooliebai:
pretty consistent bringing this up to FL. for me the big difference is east coast or west coast?
West coast would mean bad news for the east coast since the strongest winds are located in the eastern quadrant...if that makes any sense lol. And of course, east coast would mean bad news for the Bahamas. Obviously if it were to intensify into a pretty potent hurricane, then regardless of east/west coast, all of Florida is gonna be in for a rough ride.
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Quoting popartpete:
This is a tricky situation. Will it go East or West of Florida. It's only a few hundred miles, a big span for computer models. Again, anyone who poses with the dog is chill with me! I'm shopping houses in Florida, and I think I'm the only person alive willing to buy in Pinellas County!
Well don't buy, till the threat has passed. And correct with any wobbles to the left or the right makes a big difference if this stays onshore or is offshore and continues intensifying as the models are showing.
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2350. RMCF
Quoting TampaFLUSA:
Now people that live in NC will think its coming there way, SC theirs...FL ect....since I'm in Tampa its coming my way, imo....

A decent size storm with landfall just north of Tampa Bay wouldn't take much to be real bad.
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Quoting Bluestorm5:
I think it's going to hit Florida, goes over Tampa area, into Georgia, over the Carolinas, though the Mid-Atlantic, and out at Northeast.


The northwest solution after landfall that the 18 Z GFS is showing is a possiblity. Once that weakness "closes" by next weekend, the storm may not have a chance to escape northeast. I said this last week, this could be a Fay type set up - weak steering and slow movement by this time next week.
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2348. KEEPEROFTHEGATE (Mod)
2011 Storms
All Active Year


Atlantic
98L.INVEST
09L.IRENE
08L.HARVEY

East Pacific
91E.INVEST
07E.GREG

Central Pacific
06E.FERNANDA

West Pacific
97W.INVEST
96W.INVEST
95W.INVEST

Indian Ocean

Southern Hemisphere
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Quoting nrtiwlnvragn:


At the storm tomorrow morning 8:00 AM EDT



ok
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2346. ncstorm
If you dont have your house insurance, car insurance, boat insurance paid up, you betta get on it..I know in NC, once they issue a tropical storm watch for our area, you can NOT get insurance if you dont have any.
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Quoting Levi32:
A relocation under the deep convection could put Puerto Rico very close to the direct target zone again, which is another reason why they should be prepared for a substantial tropical storm. Even if it's south of them, it will be rough conditions beginning tomorrow. Dominica to Antigua and St. Kitts get this first very soon.


The local weather service said we should experience gusts over 60MPH all day sunday here in the northern leewards (st martin)
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Quoting Clearwater1:
You are the troll. Where is the discussion concerning "Irene"


Navy runs tropical weather, ATCF site, if they have it on there it's official, don't call others a troll.
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Quoting stormpetrol:
I don't care if I get called a westcaster/wishcaster, but Irene might take a similar track to Harvey only a bit further north.


LOL, I just don't see a trough pulling a system down in the Carribean north like that anyway, it's August and DOWN in the Carribean
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2342. marmark
You may know this, but if there is an active storm (and you are in the cone) you won't be able to purchase insurance and therefore not get a mortgage.
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Quoting Tazmanian:
dont they still have about 700,000 in tent city in Hispaniola



eeeeeeek
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Quoting Clearwater1:
You are the troll. Where is the discussion concerning "Irene"


It was renumbered. It's Irene. Everybody else on this blog will tell you exactly the same thing. You've just earned yourself a place on my ignore list.
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Quoting Tazmanian:
when the next recon there going too be vary busy


At the storm tomorrow morning 8:00 AM EDT
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5:00 pm Advisory Update






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Quoting dfwstormwatch:

30 hours out



from 997 too 993 too 989 too 986mb


ouch wow eeeeeeeeeeek
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2336. BVI
Bot sure many people actually aware of Irene here in the British Virgin Islands, hope it doesnt take too many people by suprise. Wonder if we will have any watches or warnings issued? ours are issued by the Government of Antiugua for the BVI
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