About Jeff Masters
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 3:06 PM GMT on August 22, 2012
Tropical Storm Isaac is lashing the entire Lesser Antilles chain of islands with heavy rains this morning, and the winds will be on the increase this afternoon as the storm heads west at 19 mph. Isaac is still a weak and disorganized tropical storm, but that is changing. The Hurricane Hunters are in the storm, and have thus far found no increase in the storm's top surface winds, which remain near 45 mph. In their 7:44 am EDT center fix, an Air Force Reserve aircraft measured a rather unimpressive center pressure of 1007 mb, and top winds at their 1000 foot flight altitude of 56 mph. The plane did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. A large area of dry air to the north of the storm, as seen on water vapor satellite loops, continues to interfere with development, and it is unlikely Isaac will become a hurricane today. Satellite loops, however, show that Isaac has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of a developing storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is becoming well-established to the southwest and northwest, but outflow is restricted on the southeast side. A large clump of heavy thunderstorms several hundred miles southeast of the center continues to compete for moisture, and is interfering with the low level inflow and upper level outflow of the storm. The intensification rate of Isaac will increase if the storm is able to integrate this clump of heavy thunderstorms into its circulation, which satellite loops this morning suggest is now beginning to happen. Radar imagery from Barbados and Martinique show plenty of heavy rain showers, mostly on the south side of Isaac where it is moister, but little spiral banding. Hurricane hunter missions are scheduled for Isaac every six hours, and a NOAA hurricane hunter research aircraft will also be in the storm, with missions scheduled every 12 hours. The NOAA jet is first scheduled to fly into the storm on Thursday afternoon, to do a large-scale dropsonde mission to aid model forecasts.
Figure 1. Morning radar image of Isaac taken from the Barbados radar at 10:15 am EDT. Image credit: Barbados Weather Service.
Intensity forecast for Isaac
The latest 8 am EDT run of the SHIPS model shows that wind shear is moderate, 10 - 15 knots, but is expected to relax by this evening to a low 5 - 10 knots. Ocean temperatures have increased to a very warm 29°C, and the storm is now over waters with a high total heat content. The lowering wind shear and warm waters should allow the storm to wall off the dry air that has been interfering with development, and also allow the storm to integrate the thunderstorm clump on its southeast side that has been interfering with low level inflow and upper level outflow. It will take some time for the increase in organization to result in an increase in Isaac's winds, and I still expect top winds of 45 - 60 mph in the Lesser Antilles Islands this evening when the core of the storm moves through. On Thursday, when Isaac will be in the Eastern Caribbean, conditions should be favorable enough to allow steady strengthening to a Category 1 hurricane. The 11 am EDT wind probability forecast from NHC predicted a 47% chance that Isaac will become a hurricane by Friday morning, and a 16% chance it will be a Category 2 or stronger hurricane then. This is a reduction in the odds given in the 5 am advisory.
Impact of Isaac on the Islands
The entire Lesser Antilles Islands chain will have a three-day period of heavy weather Wednesday through Friday. Sustained tropical storm-force winds extend out about 50 miles to the north of the center and 30 miles to the south, so an 80-mile wide swath of the Lesser Antilles will potentially see tropical storm-force winds of 45 - 60 mph this Wednesday evening. Guadaloupe, Antigua and Barbuda, Dominica, Montserrat, and St. Kitts and Nevis at highest risk of these winds.
Winds in St. Croix in the Virgin Islands will likely rise above tropical storm force on Thursday morning, and the south coast of Puerto Rico should see tropical storm-force winds by Thursday afternoon. The San Juan airport may be able to stay open Thursday afternoon and evening, but I think it is more likely they will be forced to shut down.
On Thursday night, heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic, and all airports in the D.R. will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.
Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.
Impact on Florida, Cuba, Jamaica, and the Bahamas
Florida, Cuba, Jamaica, and the Bahamas are all at high risk of receiving hurricane conditions from Isaac. The latest set of 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a westward track to a point on the south coast of Hispaniola. All of the models then predict a more west-northwest track across the island and into eastern Cuba, as Isaac responds to a trough of low pressure over the Southeast U.S. Most of the models then predict a path for Isaac along the spine of Cuba, then into the Florida Straits off the coast of Miami by five days from now. A notable exception is our best-performing model, the ECMWF, which keeps Isaac just south of Cuba, and takes the storm more to the west between Jamaica and Cuba on Saturday, then into the Yucatan Channel between Mexico and Cuba by Monday. However, this model is keeping Isaac weaker than the other models, and thus predicts the storm will have a weaker response to the trough of low pressure over the Southeast U.S. If the official NHC intensity forecast is right and Isaac becomes a hurricane on Thursday, the more southerly track of the ECMWF is not going to verify, and Isaac will spend considerable time over Cuba on Saturday and Sunday. Where Isaac pops off the coast of Cuba will be critical in determining its future path and intensity. Some models predict a more easterly exit point, allowing Isaac to move up the east coast of Florida, and potentially make landfall in the Southeast U.S. The latest 06Z GFS model run predicts a more westerly track, which would potentially allow Isaac to move up the west coast of Florida towards Tampa. Keep in mind that the average error in a 5-day forecast is 260 miles. The two most recent runs of the GFS model, at 00Z and 06Z (8 pm and 2 am EDT), gave positions for Isaac that were about 250 miles apart--the earlier run putting the center near West Palm Beach, and the more recent run giving a location between Key West and Havana, Cuba. While passage over the high mountains of Hispaniola and then Cuba will substantially disrupt Isaac and probably reduce it below hurricane strength, the storm is quite large, and should be able to re-intensify once it emerges over the Florida Straits. Waters will be very warm, near 30°C, wind shear is predicted to be light, and forecasts of the upper-level winds show the possibility of an upper-level outflow pattern very favorable for intensification. If Isaac spends a day over water, that should be enough time for it to intensify into a Category 1 hurricane, and if the storm takes a longer 2-day track over water up either the east or west coast of Florida, a Category 2 or stronger storm is possible.
Isaac is a threat to affect Tampa during the Republican National Convention, August 27 - 30, and the official NHC forecast now has Tampa in the 5-day cone of uncertainly. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 9% chance of receiving tropical storm-force winds for the 24-hour period ending on the morning of first day of the convention (Monday). I blogged about the climatological chances of a hurricane causing an evacuation of Tampa during the convention in a post last week, putting the odds at 0.2%. I put the odds of an evacuation occurring during the convention in the current situation at 3%.
Figure 2. Morning satellite image of Tropical Depression Ten.
Tropical Depression Ten forms in the Eastern Atlantic
The large tropical wave in the Central Atlantic, midway between Africa and the Lesser Antilles Islands, has become Tropical Depression Ten. The depression has an impressive amount of spin and heavy thunderstorm activity, as seen on visible satellite loops, and should be Tropical Storm Joyce by Thursday. None of the models show that TD 10 will be a threat to the Lesser Antilles Islands.
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). The GFS model has been a close second. You can view 7-day ECMWF and 16-day GFS forecasts on our wundermap with the model layer turned on. Ten-day ECMWF forecasts are available from the ECMWF web site. 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 3, the HWRF and GFDL were well behind the ECMWF and GFS in forecast accuracy in 2011, but were still respectable. The BAMM model did very well at 4 and 5-day forecasts. The UKMET, NOGAPS, and CMC models did quite poorly compared to the ECMWF, GFS, GFDL, and HWRF. For those interested in learning more about the models, NOAA has a great training video (updated for 2011.)
Figure 3. Skill of computer model forecasts of Atlantic named storms 2011, compared to a "no skill" model called "CLIPER5" that uses just climatology and persistence to make a hurricane track forecast (persistence=a storm will tend to keep going in the direction it's current going.) 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; TVCA=one of the consensus models that lends together several of the above models; CMC=Canadian Meteorological Center (GEM) model; BAMM=Beta Advection Model (Medium depth.) Image credit: National Hurricane Center 2011 verification report.
I'll have a new post this afternoon.
Jeff Masters
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
1143. LargoFl
1141. Gorty
And from Ernesto, we all know what a cyclone can do when in a favorable environment...
btw for the record, JB was right with Ernesto, intensifying close to land and remaining weak till then.
1140. Bluestorm5
1139. WXGulfBreeze
1138. gordydunnot
1137. wunderkidcayman
well right now they have East winds and just a little bit South of that they had East South East
so as they move North winds keep on shifting North hmm Isaac is an interesting system
1136. CosmicEvents
1135. hydrus
1133. gustavcane
1132. Gorty
1131. LargoFl
1130. MississippiWx
We're talking about 5+ days in advance. The average error for track at 5 days is over 250 miles. There is about 250 miles between the Euro and GFS. It's not that uncommon.
1129. Matt1989
1128. ProgressivePulse
1127. sar2401
Thankfully, if the street lights are comng on, that means they still have power. Assuming it doesn't get worse, it sounds like a strong tropical wave so far.
1125. MAweatherboy1
Well if the center reforms further south that could make the Euro's scenario more likely. That wouldn't indicate skill in the Euro however, there's no way a model could pick up a center reformation. It would just get lucky.
1124. LargoFl
1123. KEEPEROFTHEGATE (Mod)
its what i see
iam normally
not to far off the mark
1122. JasonRE
I'm confused. Is this map worth anything or is just another guess? And WHY is it so far West compared to the existing track of Isaac? I know these are just models but why is this one so far West?
1121. sar2401
Or, Mobile, AL. No one seems to be talking about that at all, but the models that have Isaac go into the Gulf are all showing landfall either in Pensacola or Mobile. If it's just a cat 1, it won't be a big deal. A strong cat 3 making a direct south hit on Mobile Bay is our nightmare scenario. It's still at least seven days off, and track and intensity mean everything, but Isaac is one of the few storms since 2005 that shows Mobile as a possible target.
1120. CaicosRetiredSailor
- Barbados
Date: Wed, 22 Aug 2012 14:52:29 -0400
The rain is here in ChristChurch. It is wild, windy, driving, heavy rain. The street lights have come on. The low grey clouds are moving very fast.
1119. HurrMichaelOrl
Based on my past experiences with strong tropical storms and low end hurricanes impacting the Orlando area (Erin '95, Irene '99, Gordon '00, Gabrielle '01, Alberto '06, Barry '07, Fay '08 and Debby '12), I expect 5-15" of rain and possibly wind gusts to tropical storm force as the center of Isaac makes its closest approach.
1118. wunderkidcayman
I think you are right
1117. MississippiWx
1116. yonzabam
Hard to make out a case for a center north of the 15N latitude line on any of the satellite images.
1115. AllStar17
1114. midgulfmom
1113. HrDelta
I am so skeptical of that solution.
I am wondering about the logic of the Euro on this one. Why do they have it going west.
1112. MrNatural
Water vapor imagery shows an ULL to the NE of TS Isaac. Looks like that system is close enough to disrupt TS Isaac. I also wonder if it is wrapping some drier air into Isaac as well. In any case, you can see a flattening of Isaac in the NE quadrant. Looks like these two systems are interacting, but I don't know for how long.
Link
1111. Chiggy
1110. hydrus
By 7:00 am, it was still strong enough to cause heavy rain and tear down hundreds of trees in Conover.[17]
In all, 29 counties in North Carolina were declared federal disaster areas, with damages in that state alone estimated at $1 billion (1989 USD, $1.87 billion 2012 USD).
1109. wpb
1107. AllStar17
1106. wunderkidcayman
1105. 1900hurricane
My guess is that the future Joyce would catch the same trough as Isaac and recurve if the run continued past 240 hours. Might clip the outer banks though. But this is all speculation upon speculation at this point. :P
1104. icmoore
Not to me.
1103. LargoFl
1102. Chiggy
1101. gustavcane
1100. CybrTeddy
No. They've been scooping out the fact that there are two circulations. All the stronger winds are on the south side, they have been investigating the northern side.
1099. NICycloneChaser
Hasn't been in the NE quadrant yet, or under the heavier convection. Should find some 40-45mph winds in there.
Even if it doesn't, I'd be willing to wager a large sum of money that the NHC wouldn't downgrade it.
1098. Bluestorm5
1097. MississippiWx
1096. CybrTeddy
Ernesto was a lot smaller, and a lot farther south that Isaac is. Storms like Dolly and Fay in 2008 also had similar problems Isaac is having.
1095. kanc2001
pfft, so you are a sidewalk south carolinian? dont even support the home team? ;)
1094. wpb
1093. seflagamma
I am trying my best to be a nice person; especially since I may be here on this blog a lot more often the next few days!!!!
but it was in my "second nature" to give a smart ass reply! LOL
but I took the high road! I will let Pottery do it.