Little change to Isaac, but intensification coming; Joyce forms

By: Dr. Jeff Masters , 3:13 PM GMT on August 23, 2012

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Tropical Storm Isaac is a large and impressive-looking storm on satellite images, but data from the Hurricane Hunters reveal that Isaac remains a minimal-strength tropical storm with 40 mph winds, as it heads westward across the Eastern Caribbean. An Air Force Reserve hurricane hunter aircraft which completed its mission into Isaac at 8 am EDT found top winds at the surface near 40 mph, and highest winds at their 5,000 foot flight level of 47 mph. A NOAA hurricane hunter aircraft flying at 10,000 feet has found top winds of 47 mph at that altitude. The Hurricane Hunters found a broad area of light winds with a central pressure of 1003 mb. The aircraft did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. There does not appear to be much in the way of dry air near the core of Isaac, as seen on water vapor satellite loops, which is a big switch from what we've seen previously. Visible satellite loops show that Isaac has a much more symmetric circular cloud pattern, and has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of an intensifying 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 an upper-level pattern of outflow supportive of significant strengthening has developed this morning, with an upper-level outflow channel now well-established to the north, and a new outflow channel opening to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and becoming more organized.


Figure 1. Morning radar image of Isaac taken from the Puerto Rico radar. Isaac's rain bands are weak, but are starting to take on a more spiraling shape.

Intensity forecast for Isaac
Isaac has consistently confounded predictions that it would intensify, but all the potential factors inhibiting intensification seem to have diminished to the point where intensification has to occur. Wind shear is low, 5 - 10 knots, and ocean temperatures are warm, 29°C, and these warm waters extend to great depth, giving the storm a high total heat content to work with. These factors, combined with the favorable upper-level outflow pattern and more symmetric cloud pattern, support intensification, and all of the intensity models except the HWRF model predict intensification of Isaac to a strong tropical storm or Category 1 hurricane by Friday afternoon. The latest 8 am EDT run of the SHIPS model predicts that wind shear will be light to moderate, 5 - 15 knots, for the next five days. The 11 am EDT wind probability forecast from NHC predicted a 34% chance that Isaac will become a hurricane by Friday afternoon, and a 6% chance it will be a Category 2 or stronger hurricane then. By Friday afternoon, Isaac will likely be close enough to Southwest Haiti that the inner core will be disrupted, and the storm will likely be a 45 - 55 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate, and the upper-level wind pattern favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane.

Impact of Isaac on the Islands
The south coast of Puerto Rico should see Isaac's heaviest rains and strongest winds beginning near 8 pm EDT tonight, with tropical storm-force winds of 40 - 45 mph potentially affecting the southwest portion of the island. The San Juan airport may be able to stay open during Isaac's passage, but with delays when spiral bands move overhead.

Heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic late tonight, and the Santo Domingo airport 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 risk of receiving flooding rains and high winds from Isaac. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a west-northwestward track over Southwest Haiti and into Western Cuba. At the 4 - 5 day forecast period for Sunday and Monday, the models have come into better agreement, and have shifted west some. Our best-performing model, the ECMWF, has now shifted Isaac's path more to the east, but still is the westernmost of the models, predicting a landfall for Isaac near the Alabama/Florida border on Wednesday. While we do still have some models predicting a path up the east coast of Florida, model consensus now favors a path up the west coast of Florida through the Gulf of Mexico. The recent reformation of Isaac's center more to the south supports the idea that Isaac will take a track more to the west through the Gulf of Mexico. Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall. The NOAA jet is scheduled to fly into the storm this afternoon, to do a large-scale dropsonde mission to aid model forecasts. These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 15% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. The latest model tracks for Isaac suggests that the trough of low pressure pulling the storm to the north will not be strong enough to give Isaac a northeastward component of motion when it crosses Tampa's latitude. Thus, Isaac will have difficulty making a direct hit on Tampa without passing over a considerable amount of land first, making a multi-billion dollar hurricane disaster in Tampa very unlikely. I put the odds of a mass evacuation occurring during the convention at 1%; a limited evacuation of people in the Tampa Bay area living in mobile homes in low-lying areas is probably about 5 - 10 % likely. I have detailed information on Tampa's storm surge vulnerability in a post from last week.


Figure 2. Morning satellite image of Tropical Storm Joyce.

Tropical Storm Joyce forms in the Central Atlantic
The season's tenth named storm of the year, Tropical Storm Joyce, has formed in the Central Atlantic. Joyce's formation on August 23 puts 2012 in a tie for second place with 1995 for earliest formation date of the season's tenth storm. Only 2005 had an earlier appearance of the season's tenth storm, when Tropical Storm Jose formed at 2 pm EDT on August 22. None of the models show that Joyce will be a threat to the Lesser Antilles Islands, but it may be a storm that will affect Bermuda. It is possible that Joyce will complicate the track forecast for Isaac 4 - 5 days from now, when the storms may be close enough together to interact.

Jeff Masters

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Quoting AAPLTrader:
LEVI has to eat crow today. For 3 days he predicted a path EAST of Florida.


Actually, he had a pretty good forecast and the predicted track is still well with in the cone of his forecast. That said, a trek up the E coast of Fl, while less likely ATM, is still possible. Someone even posted a forecast discussion that talked about further erosion of the Bermuda high.

That said, I still firmly believe that Isaac will end up between Apalachicola and the OBX. Tomorrows model runs with upper air data in them should be very useful in narrowing the projected path some.
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Good morning. Cloudy to overcast (at times) with gusty winds and a few scattered showers here in Antigua. Isaac continues on his quest to do whatever he pleases. Didn't get as much rain as anticipated. I see we now have TS Joyce which is not expected to affect the Lesser Antilles but behind her is a new wave coming off of Africa. Any long range forecasts with this one?

It is said that storms are not referred to by gender but it's kinda hard seeing male and female names and saying "it".
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Isn't this the "Dead Zone"???

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71. 7544
looking at the size of issac even with the cone being that far west most of fla will get a piece of him west and east and his size might get even larger this is not a small coverage strom as others been in the past going to the west side and est didnt get any effects so stay tuned
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Quoting HurricaneDean07:
Does anyone else realize that recon found 45 to 50 Mph winds, when Kermit was out there?

Mission 7. HH. are flying from Miami now...

They actually left Biloxi Airport not Miami. HH'ers don't fly out of Miami. They fly out of Tampa and Biloxi.
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Ok. I've had enough of the blog for now. Maybe I'll go shove some bamboo shoots up my fingernails or something.

Everyone have a good day, and try to play nice...
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Quoting serialteg:
just so you guys know:

for all this awesome, dooming satellite representation of spiral banding over puerto rico, you would think we're getting a lashing. living in the extreme central south coast, i can tell you: if i have seen .005 inches of rain its a lot.


What's going on in inches? Rincon coming back to life...

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Once the big ball of convection to the south separates, the inner core may be able to start to pull together. We'll see....been here before with Isaac and Ernesto, and they just have not pulled together. Will be interesting to read, post-season, why storms are having a tough time spinning up.
Member Since: June 23, 2006 Posts: 0 Comments: 668
Quoting 69Viking:


I live in Fort Walton Beach about 100 yards from the Santa Rosa Sound waterway. Be glad you're a mile inland, if you have any elevation you don't have to worry to much about storm surge. If you're in a newer house it should be able to handle the winds. If it looks like it's coming at you 2 or 3 days out and it gets to hurricane strength like they are forecasting make sure you board up. No reason to panic right now, being in the bullseye this far out usually means you're going to be ok. The forecast track is changing daily.


Thanks for the info. My Wife and I love Ft. Walton Beach and Destin. Now I'm hungry for Maguires Irish Pub in Sandestin.lol. We live in an apartment on the second floor. The road near us floods terribly, especially lately with all of the rain, so we worry about that quite a bit. I've never been in a Hurricane, but always thought that we would stay put for a CAT1, but maybe leave for a CAT2. Any experience with that you can help me with?
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The left line of this cone is a pretty good analog for what I think the real track will be.

Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting AAPLTrader:
LEVI has to eat crow today. For 3 days he predicted a path EAST of Florida.


Until Isaac passes South Florida and goes West of Florida he has no reason to eat crow. There is no guarantee in forecasting and there is still a lot of time before this storm gets into the GOM or the Straights South of Florida.
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So, every factor that would be conducive for strengthening is now in place, low shear, high TCHP, moist environment, moderate forward speed, no land interaction.

But I bet it doesn't.
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All NHC forecast tracks animated



Keeps nudging West
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Quoting flsky:

Best to pay the most attention to the pros.

Yeah, no one on this blog. The pros are at the NHC.
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Quoting HurricaneDean07:
Does anyone else realize that recon found 45 to 50 Mph winds, when Kermit was out there?

Mission 7. HH. are flying from Miami now...

The NHC didnt wait around for recon to report... The adivsory was too close, so they made Isaac a 40 Mph TS... Even though about 15-30 Minutes later Recon found a bunch of 45 Mph winds... and a couple areas of peak winds at 50 mph.
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Looking at the latest model runs for GFS and ECMWF, it looks like the NHC is favoring the ECMWF again. Maybe ECMWF will improve its 2012 reliability this time around? Think they'll regret moving away from the GFS at this point? It didn't work out too well for TS Debby. GFS still shows Isaac skirting the FL West Coast and entering the state near the Big Bend area which can ill afford more rain. Isn't the next GFS model run at 1pm?
Member Since: August 28, 2006 Posts: 6 Comments: 2899
Quoting AussieStorm:
Doc, why no mention of Dual Typhoons and 1 about to impact Taiwan.
Typhoon Tembin


Rainfall so far from Tembin.




And the possibility that TYPH TEMBIN will loop around and hit Taiwan for a second time!
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Thanks Dr. M. In the short-term, Issac's weak COC and relatively light winds will probably help intensification once the storm gets fully stacked because of a little less upwelling than usual going into very warm waters.

On the other side of Cuba, and if the storm tracks near the Keys and into the Gulf, here are the very warm SST's in the Florida Straits and location of the warm pools:

Link

Given the large size, and the fact that Florida will be on the dirty side, don't forget the impact on the Florida Keys; they will need to be evacuated and both coasts of South Florida (Gulf and Atlantic) will feel the huge impact of this system. Any wobbles on approach or passing the Keys may mean the difference between tropical force winds and hurricane gusts for parts of mainland South Florida.

This could be real bad for the Central Gulf coast from AL to Florida Panhandle if the storm ramps up in the Gulf.
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Don't like the sound of Jeff saying possibility of cat2 or stronger off the west coast of Florida is not out of the question. Not to mention him saying conditions are so good Isaac has to intensify. Isaac not to be faking the funk for much longer. This could well be a major off the Florida coast if things don't somehow change. Not hyping, just saying all the conditions according the good Doc are there for this to become an event for Haiti and the continental.
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Quoting ChaseyChasinStorms:


Hey neighbor. Slidell, LA here. :)



Mandeville here
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Quoting serialteg:
just so you guys know:

for all this awesome, dooming satellite representation of spiral banding over puerto rico, you would think we're getting a lashing. living in the extreme central south coast, i can tell you: if i have seen .005 inches of rain its a lot.

Those are the weakest spiral bands I've ever seen!
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Quoting AAPLTrader:
LEVI has to eat crow today. For 3 days he predicted a path EAST of Florida.
Last time i checked, there are models still east of FL, and for the past 3 days there have been models east of FL.  Calm down there guy, maybe you should stick to trading Apple stock.
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Quoting ILwthrfan:


Hey Aussie do you have a link to the radar of that site. Much appreciated!!


Link
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Quoting AAPLTrader:
LEVI has to eat crow today. For 3 days he predicted a path EAST of Florida.

Best to pay the most attention to the pros.
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Quoting ChaseyChasinStorms:


Hey neighbor. Slidell, LA here. :)
bay st.louis here gm
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what a month of august. very active. we may soon get Kirk the 11th named storm with the disturbance, that has just came off the african coast
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just so you guys know:

for all this awesome, dooming satellite representation of spiral banding over puerto rico, you would think we're getting a lashing. living in the extreme central south coast, i can tell you: if i have seen .005 inches of rain its a lot.
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Hello and Thx Doc...

12Z GFS Init:

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Does anyone else realize that recon found 45 to 50 Mph winds, when Kermit was out there?

Mission 7. HH. are flying from Miami now...
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Quoting AussieStorm:
Doc, why no mention of Dual Typhoons and 1 about to impact Taiwan.
Typhoon Tembin


Rainfall so far from Tembin.




Hey Aussie do you have a link to the radar of that site. Much appreciated!!
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Quoting CajunCrawfishhunter:
Lafayette Louisiana keeping a watchful eye out!!


Same here CCH.....sitting at work going back and forth between this site and actual work. haha Would rather just follow this all day.
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All the Gulf Casters will be struttin around like male peacocks. I wouldn't get set on a track until tomorrow morning, after the NOAA jsets take air amples and feed the data into the models....which has been the game plan all along. Can't really get too certain more than thre days out. We all know this, but the blog goes through the "Florida" "Texas" "Gulf Coast" "Tampa" battle with every storm.
Member Since: June 23, 2006 Posts: 0 Comments: 668
19: That is because it was suppose to strength...stronger=poleward. He will not be eating crow he'll change the now!
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Looks like Central FL may break get a break, if this westward trend continues. It looks as though they are weighting the track more on the Euro's westward change, rather than the 06z gfs which has it moving directly over FL. Of course, they have other data as well. After the full HH data is plugged in, maybe Central FL can relax a little more. The pan handle and other central gulf states, well that's another story.
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38. Jet2
http://maps.google.com/maps?q=28%C2%B057.45%E2%80%B 2N+82%C2%B041.90%E2%80%B2W&hl=en&ie=UTF8&ll=28.748 397,-79.991455&spn=8.499343,16.907959&sll=27.69863 8,-83.804601&sspn=17.129718,33.815918&t=m&z=7

The plant is currently under repair, but I worry about a big hurricane smacking directly into a nuclear power plant. If the trough arrives early or Issac gets powerful fast it could make the turn near the big bend.
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I find it hard to reconcile the forecast of Isaac and Joyce, if the high is what is pushing Isaac to the west, then what allows Joyce to make the hard turn to the north?
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Quoting CajunCrawfishhunter:
Lafayette Louisiana keeping a watchful eye out!!


Hey neighbor. Slidell, LA here. :)
Member Since: September 9, 2011 Posts: 0 Comments: 113
35. auburn (Mod)
Quoting wn1995:


My latest track for Isaac. Virtually no change in track... but once again calling for a cat 1 hurricane before hispaniola... and a major hurricane making landfall in the fl panhandle in 7 days.


man that is going right over my house as a TS here in Bama..I live right on the Ga Bama Line..
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Quoting Jeff Masters:
Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall.


Day-um. Guess I better shoot over to Lowes and Wal-Mart, and pull the shutters out of the shed. Bleah.

Stay away, Ivan Isaac (and Jim Cantore).
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Quoting AussieStorm:
Doc, why no mention of Dual Typhoons and 1 about to impact Taiwan.
Typhoon Tembin


Rainfall so far from Tembin.

Good point.
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Quoting FOREX:


Where 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.


I live in Fort Walton Beach about 100 yards from the Santa Rosa Sound waterway. Be glad you're a mile inland, if you have any elevation you don't have to worry to much about storm surge. If you're in a newer house it should be able to handle the winds. If it looks like it's coming at you 2 or 3 days out and it gets to hurricane strength like they are forecasting make sure you board up. No reason to panic right now, being in the bullseye this far out usually means you're going to be ok. The forecast track is changing daily.
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Like Ernesto, Isaac has been very annoying to follow.
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Still, Isaac's future depends on the interaction it has with those 2 ULLs mixing dry air..... until when it will keep Stuck in there?...

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"Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and taking on a more spiral configuration."

Those spiral bands must be awfully weak. The convection does look awesome, but I don't see the organization Dr. M seems to be seeing.
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Thanks Dr. M, IMO Isaac will be lucky to even make it to hurricane strength by the time it reaches Haiti, though if it gets a solid core i so no reason why he cant rapidly intensify.  It appears now that spine of FL may be spared of Isaac, which is good news, but the panhandle is still soaked from rains in the past month. 
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Doc, why no mention of Dual Typhoons and 1 about to impact Taiwan.
Typhoon Tembin


Rainfall so far from Tembin.


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My latest track for Isaac. Virtually no change in track... but once again calling for a cat 1 hurricane before hispaniola... and a major hurricane making landfall in the fl panhandle in 7 days.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.