Isaac is strengthening

By: Dr. Jeff Masters , 2:58 PM GMT on August 24, 2012

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Tropical Storm Isaac is strengthening. An Air Force Reserve hurricane hunter aircraft measured surface winds of 60 mph on the east side of the center, about 170 miles south of Santo Domingo in the Dominican Republic, at 8:40 am EDT this morning. Winds at the aircraft's flight level of 5,000 feet were hurricane force, 76 mph. The surface pressure remained fairly high, at 1000 mb. Tropical cyclones have a warm core, and the Hurricane Hunters typically find that a storm's lowest pressure is also where the warmest temperature are. However, this morning's flight found that Isaac was still disorganized, with the storm showing almost no evidence of a warm core. Isaac's warmest temperatures were displaced 75 miles to the west of where the lowest pressure was. There were no signs of an eyewall beginning to build. Infrared and visible satellite loops show that Isaac is somewhat asymmetric, with a large band of intense thunderstorms to the east, separated from the core region. This is interfering with both the storm's low-level inflow and upper-level outflow, but the band appears to be dying out. An analysis of upper level winds from the University of Wisconsin CIMSS shows an upper-level outflow channel well-established to the north, and an intermittent outflow channel to the south.


Figure 1. Evening shot of Tropical Storm Isaac taken on August 23, 2012, by the NOAA Hurricane Hunters.

Isaac's rains
Radar imagery from Puerto Rico shows that Isaac is dumping some very heavy rains to the south and east of the center. Ponce, Puerto Rico had a wind gust of 37 mph this morning as a heavy band of rain moved through, and radar-estimated rainfall amounts are in excess of 7 inches for the region just north of Ponce. Power outages to 2,000 homes have been reported in Puerto Rico this morning. NOAA buoy 42085 offshore from Ponce reported a wind gust of 54 mph near 9 am EDT this morning. Rainfall estimates from microwave satellite instruments suggest that Isaac's heaviest rains are to the south of the center, and that the Dominican Republic and Eastern Haiti will escape the worst of Isaac's rains. Haiti's southwest peninsula and Eastern Cuba should suffer the heaviest rains.


Figure 2. Radar-estimated precipitation from the Puerto Rico radar shows the region near Ponce has received up to 7" of rain as of 10 am EDT August 24, 2012.

Latest model runs for Isaac
The latest set of 00Z and 06Z (8 pm and 2 am EDT) model runs have come into better agreement, thanks to the dropsonde mission by the NOAA jet yesterday afternoon and evening. Isaac should move over Haiti's southwest peninsula and then eastern Cuba, then track along the spine of Cuba before popping off into the Florida Straits on Sunday. A trough of low pressure will then pull Isaac to the northwest, and then north, towards the Central Gulf Coast. Landfall locations range from Mississippi (06Z HWRF model run) to the Florida Panhandle south of Tallahassee (06Z GFDL model run.) It is possible that the trough of low pressure pulling Isaac to the north may not be strong enough to pull Isaac all the way to the northeast and out to sea, and the ECMWF model indicates that Isaac could stall out after landfall over the Tennessee Valley for several days.


Figure 3. Predicted 5-day rainfall total ending at 2 am EDT Wednesday August 29, from Tropical Storm Isaac. Graphics were generated from the 6Z (2 am EDT) August 24, 2012 run of the HWRF model. Image credit: Morris Bender, NOAA/Geophysical Fluid Dynamics Laboratory.

Intensity forecast for Isaac
Isaac has not intensified as much as predicted, and I think that the storm's very large size is partially responsible for that. It's tough to spin up as much atmosphere as Isaac is attempting to do very quickly. Conditions remain favorable for intensification today, with wind shear low, 5 - 10 knots, ocean temperatures warm, 29°C, and dry air mostly mixed out of the storm's core. The large band of intense thunderstorms to the east, separated from the core region, appears to be dying out now, which will help the storm grow more organized. The storm's structure has improved considerably between 9 am - 10 am EDT, with a fairly tight center forming, exposed to view, on the north edge of Isaac's heaviest thunderstorms. A curved band of heavy thunderstorms is now trying to wrap around this center to the northeast, and this band will bring very heavy rains to Haiti and the Dominican Republic this afternoon. I expect that the Hurricane Hunters will observe a partial eyewall in their vortex reports between 2 - 4 pm EDT this afternoon. The storm's large size and disorganized structure suggests that Isaac will be able to intensify only slowly today, and will have top winds of 70 - 75 mph before encountering Southwest Haiti and Eastern Cuba tonight and Saturday. Isaac will likely be a 50 - 60 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. The upper-level wind pattern favorable may be quite favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm--though the models disagree on whether or not this anticyclone will set up directly over Isaac or not. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane. It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.

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 17% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. Tampa is in the NHC cone of uncertainty, though near the edge of it. At a minimum, Tampa will receive very heavy rains and wind gusts in excess of 40 mph. Isaac is going to be hard-pressed to bring hurricane-force winds to the city, though, since any path that takes it close to Tampa would keep the storm too close to land for significant intensification to occur. I put the odds of a mass evacuation being ordered for Tampa during the convention at 1%. I have detailed information on Tampa's storm surge vulnerability in a post from last week.

Invest 97L off the coast of Africa
A tropical wave that moved off the coast of Africa on Thursday has been designated Invest 97L by NHC this morning. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear of 10 - 20 knots. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Sunday morning. The 8 am EDT SHIPS model forecast predicts that 97L will track west-northwest over the next few days, and encounter a region of high wind shear associated with an upper-level low on Monday and Tuesday. This low may be capable of tearing the storm apart, as happened to Tropical Storm Joyce. None of the models currently foresee that 97L will affect the Lesser Antilles Islands, but 97L may pass near Bermuda 7 - 8 days from now.



20th anniversary of Hurricane Andrew
Today, August 24, is the 20th anniversary of Hurricane Andrew, which hit South Florida as a Category 5 hurricane with 175 mph winds--one of only three Category 5 hurricanes ever to hit the U.S. With Isaac churning through the Caribbean this week, I didn't have time to prepare a special post on Andrew, but our Hurricane Andrew archive page has links to satellite and radar images, newspaper headlines, and 49 YouTube videos. Here's an additional link for an Andrew damage video shot by wunderblogger/storm chaser Mike Theiss, when he was 14 years old.

Jeff Masters

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Quoting floridaboy14:
it wont open. what motion is he heading


Try again or update your flash player.
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460. tessa
I was looking at the WV Loop and it shows alot of dry air in the eastern GOM...will that move away or will Issac push through it?
Thanks
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Quoting sar2401:


Reed, you're saying that only Florida is at risk and anywhere west of Florida is at no risk? Like AL, MA, or LA? You're either mistaken or kidding.


There is no way a storm can bust through a ridge like that.... you should read again.
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Ok so I might be a little slow here but.... I live in Ft. Lauderdale and have been watching this storm for days... I don't want to wait too long before preparing... I have supplies but want to know when will I know if I should put up the shutters? GFS has been shifting the past couple of days and I have no idea if it coming here as a cat 1 or higher... if we will feel that type of winds here...
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Here is the latest GFS animation

Member Since: August 7, 2010 Posts: 0 Comments: 1937
456. yoboi
Quoting MississippiWx:
Buoy directly underneath of Isaac is reporting a 999mb pressure reading. Slowly strengthening.


yep starting to crank...
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Quoting wunderkidcayman:


yes but we are past that recon and I was talking about that thing that looks like an eye type feature on vis that kinda agrees with 16.3N 70.8W I followed it for the past couple of frames and its either moving W or that could just be a wobble to the W

either way need to wait on recon it should betaking off in about an hours time



this maybe correct still need to wait on recon lift off is about an hour from now
The storm is right on track,according to the Official!! National Hurricane Center track!!,according to this official track right now Isaac is not going to get near any island south west of Cuba!!.
Member Since: August 28, 2006 Posts: 0 Comments: 624
..how styorm surge affects tampa bay
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Quoting kshipre1:
seems like so much has changed with path of Isaac. who knows....track could change back west


That's why I never take it for a sure bet any further than the track for two days. I'm still thinking around Mississippi landfall but who really knows?
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LMAO... 12z GFS wants to make 2006 Ernesto out of Isaac.
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Quoting WxGeekVA:


Seems like Isaac is finally getting himself together. Afternoon everyone.


IMO we'll have Hurricane Isaac later today. Only 15MPH away.
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Quoting pottery:
What time does the Crow model come out ?


lol
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Quoting GetReal:
MoonLC posted this a couple of minutes ago, but the blog is moving so fast many must have missed it...

Check out this NEW view if Isaac that leaves NO DOUBT to his current location of the center in the motion...

Some may be surprised at the detail.... Link
it wont open. what motion is he heading
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Quoting GetReal:
MoonLC posted this a couple of minutes ago, but the blog is moving so fast many must have missed it...

Check out this NEW view if Isaac that leaves NO DOUBT to his current location of the center in the motion...

Some may be surprised at the detail.... Link

Saw that.
A very nice one.
Member Since: October 24, 2005 Posts: 0 Comments: 24400
Quoting MississippiWx:


Charley is in no way similar to this storm. Charlie was already a Cat 3 when he made landfall on Western Cuba, which has relatively flat land when compared to Haiti and Eastern Cuba. It wasn't that amazing for Charley to strengthen quickly back into a major considering those facts.



That's a denialist comment, considering Charley was about the same strength when it was in the closest analog position as Isaac.

The official intensity forecast is based on statistics and dynamics assuming the track forecast is correct.

If the storm takes the western side of the cone, which is very close to both Charley and Climatology for a storm in this position, then it would probably be much more intense than the center line of the cone.


Remember, this is not an exact science, in spite of the advanced models and technology involved. The intensity forecast is often wrong by a category or two beyond 48 hours, and the NHC and FEMA usually tells people to prepare for a category or two higher than the forecast, just in case...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
This was Hurricane Charley as a 45 mph 1005 mb tropical storm:

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Quoting HoustonTxGal:


ooops, my bad, sorry


It's all good.
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444. yoboi
Quoting Articuno:
I repeat:
Abrams was talking to the mayor of KW and they said they don't evacuate unless Cat 3 or higher.


???? your joking???
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443. 7544
eoc imn miami making a speech now they must have see the gfs lol
Member Since: May 6, 2007 Posts: 0 Comments: 6860
Quoting interpreter:
Sure doesn't look like Isaac is moving very much. Might be stuck in the proverbial rock and a hard place. If that is the case it can go in almost any logical direction once it does start moving.


I have been looking at that as well; the coc is still on the move but he has the appearance of slower movement as those bands are trying to wrap around out of the S and SE quadrant as the pressure drops a bit. He is trying to consolidate.
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Seems like Isaac is finally getting himself together. Afternoon everyone.
Member Since: September 3, 2011 Posts: 13 Comments: 3475


LAKELAND | Polk County emergency preparations began cranking up Thursday as Tropical Storm Isaac churned south of Puerto Rico on a projected path that leaves Florida's west coast vulnerable to heavy rains and hurricane-force winds.


Facts

SANDBAGS

Polk County residents can pick up sandbags at these locations starting at noon today. Each household can take 25 to 30 bags to protect against floodwater. Bring a shovel.
Providence Fire Station, 8936 U.S. 98 N., Lakeland.
Mulberry maintenance facility, 900 N.E. Fifth St..
Saddle Creek Fire Station, 3325 E. Main St., Lakeland.
Jan Phyl Fire Station, 333 American Spirit Blvd., Winter Haven.
Fort Meade maintenance facility, 1061 N.E. Ninth St.
Cottonwood Fire Station, 126 Cottonwood Drive, Davenport.
Solivita Fire Station, 1201 Cypress Parkway, Poinciana.
Golfview Fire Station, 2902 State Road 60 E., Lake Wales.
Indian Lakes Estates Fire Station, 221 Hogan Lane.
Bartow Fire Station, 110 E. Church St.



To prepare for floodwater, the county will hand out sandbags at fire stations across the county starting at noon today.

The county is watching forecasts before deciding whether to open shelters, said Brad Ruhmann, a county spokesman. The decision isn't made lightly: Most of the shelters are school campuses. Opening them would mean canceling class for students who just started the new school year on Monday.

Shelters for the disabled need at least 72 hours advance notice before opening; other shelters can open on shorter notice.

Polk County school officials did not decide Thursday whether to reschedule or cancel campus activities. In Lake Wales, charter students will receive a letter today that says if county schools close, theirs will too.

Ruhmann said residents should start making their own preparation — especially where they will stay.

"We're going off a forecast that is continuously changing," he said. "And we have the weekend thrown in the mix, so people might not be paying as much attention,"

Saturday the county will open its emergency operations center. Officials will begin round-the-clock monitoring Sunday, when the National Weather Service predicts the storm center will move northwest from Cuba into the Gulf of Mexico.

Isaac is still too far away to know for certain whether it will track eastward and hit the west coast of Florida and how strong it will be when it enters the Gulf, said Dennis Feltgen, a National Hurricane Center spokesman.



















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Quoting alvarig1263:


I believe this was from yesterday. I don't think they've updated the 12Z yet today. I might be wrong though.


ooops, my bad, sorry
Member Since: September 18, 2007 Posts: 0 Comments: 1074
Hey Keeper - I hope those aren't the storm surge maps :P
Quoting KEEPEROFTHEGATE:

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437. CJ5
Isaac is still having a hard time closing himself off. He will need to tighten up more if he wants to be a force once in the gulf.
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Quoting reedzone:
The storm should begin a northwesterly movement, clipping Haiti, moving through flat terrain of Cuba, which shouldn't weaken the storm rapidly as originally thought. Potential for a Major Hurricane to hit Florida is there. Charley in 2004 went from a Cat 2 to a 4 in 2 hours. Conditions appear to be RIPE for further development after reaching the Gulf of Mexico. Everyone from the Keys, East/West Coast of Florida, Panhandle of Florida needs to review their Hurricane plans and start preparations for the worst. Anywhere west of Florida, your safe. A storm cannot bust through the corner of a developing ridge, laws of physics and gravity don't work that way. East of 85W Isaac will stay.


Reed, you're saying that only Florida is at risk and anywhere west of Florida is at no risk? Like AL, MA, or LA? You're either mistaken or kidding.
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MoonLC posted this a couple of minutes ago, but the blog is moving so fast many must have missed it...

Check out this NEW view if Isaac that leaves NO DOUBT to his current location of the center in the motion...

Some may be surprised at the detail.... Link
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TWC can't win. Often I hear complaining that their programming is for the masses and that they should cover what's happening in real time way more. Now I hear they are focusing on Isaac too much and should go back to regular programming. TWC would be wise to have two channels. One for the masses and their programming they like so much and one for the junkies who love the science and real time info. Not talking about just you Opal, what you stated has been stated at least several times by others yesterday.
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Buoy directly underneath of Isaac is reporting a 999mb pressure reading. Slowly strengthening.
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Quoting HoustonTxGal:
12z ECMWF



I believe this was from yesterday. I don't think they've updated the 12Z yet today.
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Tropical Cyclone Heat Potential:



Sea Surface Temperatures:



Chance for intensification just before landfall looks good in South FL., if the GFS track were to verify.
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What time does the Crow model come out ?
Member Since: October 24, 2005 Posts: 0 Comments: 24400
429. Relix
Raining cat and dogs here in Puerto Rico. Faaaar more than when the system was close.
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Quoting HoustonTxGal:
12z ECMWF


stop posting models that are 24 hrs old.
Member Since: August 6, 2007 Posts: 0 Comments: 693
Quoting chevycanes:
999 mb



Great find. I expect the pressure to be even lower once the HH aircraft gets in there in the next few hours.
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Quoting MississippiWx:


Charley is in no way similar to this storm. Charlie was already a Cat 3 when he made landfall on Western Cuba, which has relatively flat land when compared to Haiti and Eastern Cuba. It wasn't that amazing for Charley to strengthen quickly back into a major considering those facts.

hey WX how do you think we will fare?
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GFS has it headed toward S.E. Florida.
Member Since: September 27, 2007 Posts: 1 Comments: 21432
12z ECMWF

Member Since: September 18, 2007 Posts: 0 Comments: 1074
12Z GFS...... in an angry mode again!!!!!!!!!! Why there is no high to push systems to the west. The islands will become desert OMG I hate that and hope things change and turn wetter for us

ERNESTO + TD7 + ISAAC = BUST over my area
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I live in downtown Tampa. The flooding can be so bad just from a thunderstorm that these model shifts are unsettling. It will be interesting to see how this plays out.
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Quoting MississippiWx:


Charlie is in no way similar to this storm. Charlie was already a Cat 3 when he made landfall on Western Cuba, which has relatively flat land when compared to Haiti and Eastern Cuba. It wasn't that amazing for Charley to strengthen quickly back into a major considering those facts.

It was a small storm as well which makes quick strengthening not that unusal. They also weaken more quickly as well.
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999 mb

Member Since: August 6, 2007 Posts: 0 Comments: 693
east, west, east, west...the wait and see is killing me
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Reed,you may need to adjust your track father east as Issac will be stronger than a one after crossing Eastern Cuba.
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seems like so much has changed with path of Isaac. who knows....track could change back west
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416. skook
Quoting drg0dOwnCountry:
ECMWF model indicates that Isaac could stall out after landfall over the Tennessee Valley for several days.

This is probably the greatest danger from Isaac.



That could be a great danger, but I would also say the area north of Tampa, towards the panhandle would also be in great danger just from the rain alone. This area has been in a flood watch, with river warnings pretty constantly since Debbie hit months ago.
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Quoting alvarig1263:


According to the latest 12Z GFS model run at 66 hours we're going to get pounded by the center. At least by a Cat 1. or maybe even Cat. 2 hurricane. The GFS shows Isaac going over a lot more water, rather than going over Cuba.



I agree the potential is there for cat 1 or 2 but we will have to see what Issac looks like after traversing Cuba before i get too excited. Right now is the time to be prepared as we are only three days out now.
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Those folks in Port Royal Hate when hurricanes try to ruin their golf outings :-P Im just a tiny bit north of them in Estero fl..everyone here it seems is preparing as well. Stay Safe Everyone!
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Quoting RTSplayer:


Not really.

That would be a blessing.

Mississippi River is at or near record lows in many places. Near Tennessee it's lost 90% of it's average width and probably 95% of it's average flow volume.

Barge traffic has been suspended or spotty in many locations between Tennessee and Louisiana, with the river depth as little as 4ft in some locations.


I wouldn't know for sure, but I assume both the Missouri and Ohio Rivers are very low, so a stall would be welcome.
hmmm ok.
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Sure doesn't look like Isaac is moving very much. Might be stuck in the proverbial rock and a hard place. If that is the case it can go in almost any logical direction once it does start moving.
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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.