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 , 8:34 PM GMT on August 22, 2012
Tropical Storm Isaac continues to maintain top winds of just 45 mph as its center prepares to move through the Lesser Antilles islands late this afternoon and early this evening. The entire Lesser Antilles chain of islands is receiving heavy rains from Isaac, with Martinique picking up 1.46" of rain as of 2 pm EDT, and St. Lucia receiving 1.49". However, Isaac is not yet generating much in the way of tropical storm-force winds, and none of the islands had received winds in excess of 30 mph as of 4 pm EDT. During their storm penetration to obtain their 2 pm EDT center fix, an Air Force Reserve aircraft measured top surface winds of just 40 mph, and a central pressure of 1004 mb. Top winds at their 5000 foot flight altitude were 49 mph. Isaac is undergoing significant changes to its structure. The plane found the center had become a broad, elongated oval that extended 40 miles from NW to SE. The old center, fixed at 2 pm near 16.1°N, and closer to the dry air to Isaac's north, is being challenged for dominance by a new center that is attempting to form near a burst of heavy thunderstorms at 15.5°N. The Hurricane Hunters' latest fix at 3:50 pm EDT put the center near 15.9°N, a southwards shift of about 17 miles. The resulting battle between centers is giving Isaac a rather odd spiral rectangular shape, as seen on visible satellite loops. The Hurricane Hunters 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 Isaac will not be able to begin strengthening until it resolves the battle between it two competing centers, and casts out the dry air infiltrating it. This is going to take at least a day, since Isaac is a very large storm, and it takes more time to spin up a big chunk of the atmosphere. Radar imagery from Barbados and Martinique show plenty of heavy rain showers, mostly on the south side of Isaac where it is moister. There has been a modest increase in spiral banding since this morning.
Figure 1. Afternoon satellite image of Isaac, showing its odd spiral rectangle shape.
Latest model runs for Isaac
The latest set of 12Z (8 am EDT) model runs are very similar to the previous set of runs, which I discussed in detail in this morning's post. The models show a westward track to a point on the south coast of Hispaniola. Isaac's center shift to the south may require some modest adjustments to the south and west for the models. This would result in the storm spending a few hours less time over Hispaniola, and more time over or just south of Cuba. This would slightly decrease the risk to the Dominican Republic, the east coast of Florida, and the Bahamas, but increase the risk to the west coast of Florida. The ECMWF--our best performing model over the past two years--continues to be an outlier among the models. It predicts that Isaac will track just south of Cuba, cross the western tip of Cuba on Monday, then head north towards an eventual landfall in Louisiana. 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, and at this point, we don't know it its more likely that Isaac will go up the east coast of Florida, the west coast, or straight up the peninsula over land. At this point, I'd put the odds at:
40% chance of a track through the Gulf of Mexico, west of Florida
25% chance of a landfall in South Florida, and a track mostly over the Florida Peninsula
35% chance of a track along the east coast of Florida
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? 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 2, 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 2. 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 in the morning.
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
4501. bappit
12:36 AM GMT on August 25, 20124500. ftlaudweathermaster
6:05 PM GMT on August 24, 20124499. HuracanTaino
11:11 PM GMT on August 23, 20124498. Stormchaser121
9:56 PM GMT on August 23, 20124497. hydrus
4:29 PM GMT on August 23, 20124496. hydrus
4:13 PM GMT on August 23, 20124495. canehater1
3:39 PM GMT on August 23, 2012will ever get symmetrical wind fields
Link
4494. panamasteve
3:37 PM GMT on August 23, 20124493. seer2012
3:36 PM GMT on August 23, 20124492. 12george1
3:35 PM GMT on August 23, 20124491. presslord
3:30 PM GMT on August 23, 2012maybe it's just a benign comment on a blog
4490. SrChiefFan1
3:29 PM GMT on August 23, 2012yea, us Redneck Riveria folks in the Panhandle aren't part of Florida....just saying...
4489. lottotexas
3:28 PM GMT on August 23, 20124488. emcf30
3:28 PM GMT on August 23, 20124487. guygee
3:26 PM GMT on August 23, 2012Validity?: unknown.
4486. gordydunnot
3:26 PM GMT on August 23, 2012Does anyone think this is going very far in gulf? Really
4485. moonlightcowboy
3:26 PM GMT on August 23, 2012Evidently, you've not been following any of my previous posts.
4484. LightningCharmer
3:25 PM GMT on August 23, 20124483. Chiggy
3:23 PM GMT on August 23, 2012AGREE
4482. coffeecrusader
3:23 PM GMT on August 23, 20124481. Chiggy
3:23 PM GMT on August 23, 2012In that pics I posted for ALL Aug storms in the vicinity of Issac, only 4 out of about 30 hit Fl and none of them were more than Cat-1 that hit FL. That is ALL I am saying.. no use in putting up rare example of storms going from west to east :)
4480. wunderkidcayman
3:22 PM GMT on August 23, 2012I dissagree with the current location however I will wait for HH RECON to fly in but I think they will find it further S
4479. WthrWonk
3:22 PM GMT on August 23, 20124478. LightningCharmer
3:20 PM GMT on August 23, 20124477. jeffs713
3:19 PM GMT on August 23, 2012I wasn't talking about Isaac at all. I was talking about using climatology as a primary method of estimating landfall or storm track. To be more specific, I was talking about Hurricanes Paloma, Omar, and Lenny.
4476. Tribucanes
3:19 PM GMT on August 23, 20124475. hurricanejunky
3:18 PM GMT on August 23, 2012Yeah I know but this convective burst is HUGE. Still dealing with dry air even with that...I wonder how long it'll take to get past that...
4474. Elena85Vet
3:18 PM GMT on August 23, 2012:facepalm:
4473. stoormfury
3:18 PM GMT on August 23, 20124472. Chiggy
3:17 PM GMT on August 23, 2012Sure..I didn't say "zero chance" BUT the picture was indicative of the odds on FL landfall..! It's a good statistics since it is all storms formed in the past 150 years in Aug in the vicinity of Issac.
You need to pull up a similar statistics for storms in the vicinity of Wilma (presume that what you are referring to) going from West to East...
4471. serialteg
3:17 PM GMT on August 23, 2012its happened a few times in recent years actually
omar, lenny
west-to -east plots
EXTREMELY awesome for surfing.
4470. MSGIRL1972
3:17 PM GMT on August 23, 2012So should we start watching closer over here in Ms? My first time to ever post, just love reading everyone elses post. This site really is very good cause it helps people to prepare.
4469. SSideBrac
3:16 PM GMT on August 23, 2012Is that your "forecast" or a throw-away scare mongering line?
4468. mitthbevnuruodo
3:16 PM GMT on August 23, 2012But they're all over the place still really. Prob is, even with better computer models and having the old data to compare, hardly anytime will the conditions be exactly the same as for a previous storm, so still so much chance with the forecast still. Even if it's just the difference in how strong a ridge is, or ridge to storm strength etc, can make it track diff than a previous storm. I'm still waiting to see if he takes that turn. Someone from Jamaica was on here this morning very concerned as no one was preparing there and no official word it seems, despite being on the track of some models.
4467. FOREX
3:16 PM GMT on August 23, 2012lmao
4466. GeorgiaStormz
3:15 PM GMT on August 23, 2012XTRP is not a model, it an extrapolation, just extrapolating where this would go if it continued at the current vector
4465. FOREX
3:15 PM GMT on August 23, 2012Where in the Panhandle is your house? I live in Panama City Beach exactly one mile from the gulf. Given my Wife and I live paycheck to paycheck right now, a direct hit here would really hurt us.
4464. bappit
3:14 PM GMT on August 23, 2012Wrong loop.
Here.
4463. Neapolitan
3:14 PM GMT on August 23, 20124462. mynameispaul
3:14 PM GMT on August 23, 2012good morning chasey. glad isaac isn't coming to la/tx. the weather here is fairly comfortable now
4461. HrDelta
3:14 PM GMT on August 23, 2012Hey, I said that yesterday. With a great dollop of anger too.
So, here's a question. Why did Issac weaken overnight?
4460. CajunCrawfishhunter
3:14 PM GMT on August 23, 20124459. WunderAlertBot (Admin)
3:13 PM GMT on August 23, 20124458. AussieStorm
3:13 PM GMT on August 23, 2012Why does that loop say 2011??
4456. galvestonhurricane
3:13 PM GMT on August 23, 2012Where have I heard that before? Oh yeah, Ernesto...
4455. Category5HitsFl
3:13 PM GMT on August 23, 2012I am expecting this Westerly trend to continue, since this storm does not seem like it can get its act together. The fact that it sped up in the last advisory and the lack of any strengthening, actually it weakened a bit, is an indicator that this Western trend will continue.
I think the Euro model picked up on this Western trend, and now it seems to be panning out as we go further into the forecast period. I am thinking this it will go on a more NW course as it enters the gulf with the Trough present in the region. I am then expecting it move into the coast somewhere around LA/MS/AL just given the trend so far.
I don't see this as an East Coast event, and just don't see the Bermuda High weakening as much as they it will or the trough being that deep or strong. I think we ought to see a track that is somewhere between Katrina and Ivan, but now its all a wait and see game.
4454. serialteg
3:13 PM GMT on August 23, 2012no, but even worse, katrina-esque...
4453. weathermanwannabe
3:13 PM GMT on August 23, 20124452. sunlinepr
3:12 PM GMT on August 23, 20124451. mikatnight
3:12 PM GMT on August 23, 2012Last Updated On 8/23/2012 3:00:00 PM GMT