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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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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A couple of interesting data points:

1) When Isaac arrives in FLA, he'll be doing so just before the full moon. This will increase the impact of any storm surge.

2) I was gassing up my SUV this morning, and a guy in in front of me had his F250 loaded up with probably 100 gallons of different size gas cans. The whole bed of his truck was covered with gas cans. Probably cost him close to $500 to fill everything up.
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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.


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.

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Quoting TomballTXPride:


Charlie though was small and compact, more susceptible to RI. Isaac isn't. I don't expect anything higher than a category 1 for the initial Florida landfall whether that's the Key's, Everglades, or Miami-Dade County side.


Wilma was a very large system and went from a TS to a full blown Cat 5 in 24 hours.

Just saying.
Member Since: September 2, 2006 Posts: 110 Comments: 6874
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Quoting TomballTXPride:


Charlie though was small and compact, more susceptible to RI. Isaac isn't. I don't expect anything higher than a category 1 for the initial Florida landfall whether that's the Key's, Everglades, or Miami-Dade County side.


My thoughts right now are Category 1-2.
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IMHO - not the most opportune time for Cayman Govt to run a Hurricane Exercise - especially given text of the last message regarding "Seeking Shelter Immediately"
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The consensus track will probably trend toward the west as the next EURO model comes in.
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off to the gym to work off some of this storm stress :)
back in an hour
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399. 7544
Quoting hurricanejunky:


Yet the NHC nudges the cone even a little further west. Hopefully giving up on the GFS doesn't bite them in the ass again. I thought they would have left it right where it was but they're the experts so...


plus 1 maybe the 5pm will shift back to the east
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Quoting drg0dOwnCountry:


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.
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Quoting goldenpixie1:
Please help me sort this out - what's the dirty side of the storm? And in the case of Isaac and it's current track - what cities would be on the dirty side? We've been arguing this out at work and can't come to a consensus.Thanks for your help!


It depends on where you are, really. The worst 'side' of the storm is the side where the winds are coming onshore from the ocean, vs. circulating back offshore from the land side. If you're on the Atlantic coast, you'd normally rather be south of the storm than north of it, because the onshore wind will be on the north (NW) side of the storm. On a N-S line of the Florida Gulf coast, you'd want to be north of the storm vs. south of it, if it's landfalling from the Gulf side - because the onshore winds would be on the south (SE) side of the storm. On an E-W line of the Gulf coast, you want to be west of it vs. east, strongest portion is NE quad. N-S line of TX Gulf coast or Mexico would be same as Atlantic.

Storm circulation is the same in all cases, it's just how the land is oriented in relation to it that would make it different.
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Anybody here the winds in south florida I wonder how strong Isaac can get maybe a cat 3 or maybe more in those warm waters near the florida keys
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Quoting clwstmchasr:


Not moving west or south of west anymore. Look at the fixes from the Hurricane Hunters. They clearly show the direction. The weakness is there and it is moving in the general direction of Eastern Cuba.


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

Quoting RTSplayer:
Colorado State's tracker has re-positioned itself to roughly a compromise between my fix and the NHC fix.




Not that it matters much, but I do point out this tool bounces around a lot and it tends to north cast stuff, so this correction may be overshooting back to the south, but it clearly does not like the NHC position either.


this maybe correct still need to wait on recon lift off is about an hour from now
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Lighthouse Point here
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Weather Channel!!! WHAT IS WRONG WITH YOU, I APPRECIATE YOUR COVERAGE OF THE STORM, but covering it EVERY WAKING MOMENT LIKE KATRINA IS ABOUT TO WIPE OUT NEW ORLEANS AGAIN, COME ON!!!! THIS IS NOT 2004 or 2005 WHERE ALL HELL HAD BROKEN LOOSE!!!!!!!! I HAVE TO ADMIT, I'm GETTING KIND of SICK of THIS!! I estimate that they are spending 90% of their air time talking about Isaac, it's a tropical storm and it isn't even going to affect the US for another two days or so!!!!!!!!!!!!! They might have a reason to cover it as much as they are now when it is over Cuba or the Gulf, but not now, not now.....
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Quoting Jedkins01:



I really, really highly doubt we will see a worst case scenario for Tampa. Here is why. When you consider the type of steering that will be in place with Isaac, I do agree that track will shift much closer to Tampa, however a hard right turn in the gulf is very unlikely with this scenario. For this storm to make a direct hit on the Tampa Bay area, it would likely have to first directly hit South Florida, which could still happen, but by then we would just have a butt load of rain and gusty winds. Nothing we aren't used to here in Tampa Bay, torrential rain, tropical storm force winds and tornadoes are common and are part of living here.

I do believe Isaac will take a turn into the eastern gulf, but I don't see how it could impact Tampa as a serious threat. Let's not start letting fear and hype get the best of us.
I'm not saying the worst case scenario is impossible, I mean, if Isaac were to rapidly deepen in a Katrina or Charley way, it could suddenly hook into Tampa. But lets remember the odds of that happening are extremely low. With that said, we must consider all possibility, but not get fearful or induce. Hype, the local MET Denis Phillips would agree with me right now, and that's why I follow his style, its sound science.


I'm not accusing you of hype, I know you are not that way, I'm really posting this for the sake of all bloggers, just be careful that other Floridians here don't think you are telling them that Tampa will be meeting it's doom in a few days.


At this point the storm could still even strike New Orleans. Now if the NHC has say a major hurricane consistently striking Tampa bay of this weekend, which I don't think will happen, then people need to start preparing for the big one, but even with that, people must still remain as calm and collective as they can.


I think youre somewhat off base.... If the new GFS verified, we would be looking at some very serious consequences here in Tampa Bay. Maybe not "worst case scenario" but much more than the "usual" storms we are accustomed to.
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HR 120 PRECIP TOTALS FINAL

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Quoting canehater1:
For now the bullseye is on Destin, Fl but due to uncertainty with track and intensity everyone from
Ms coast eastward to Bahamas should be alert.


Excellent advice. There is no straight line path for Isaac at this point, but I am hoping that we'll have a better fix on his track tomorrow morning. I'm just a bit west of Destin. My biggest concern at this point is that he doesn't blow up too much over the Florida Straights and eastern GOM - he's already pretty darned big, and putting more octane into him would be a bad thing.

We remember Ivan only too well.
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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.


Right along with my thinking.
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Quoting MississippiWx:
If Isaac takes the GFS track, he most likely won't strengthen into more than a Cat 1 hurricane. Awful lot of land interaction to expect more than that...
adjust that track 50 miles and its over water over a longer period of time. we wont know until isaac moves into the gulf. if he takes the most western track, how strong could he get
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Quoting trey33:



Downtown Tampa here


West Bradenton, near the water...
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Quoting weatherman12345:
When does 12z Ecmwf come out?
12Z = 8 am EDT


Goodnight all.
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Quoting ch2os:


Ft Pierce


Palm Harbor
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382. FLMK
Quoting ch2os:


Ft Pierce


Winter Springs here. Parents in North Port, Brother in North Port, daughter in Eustis.
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If Isaac takes the GFS track, he most likely won't strengthen into more than a Cat 1 hurricane. Awful lot of land interaction to expect more than that...
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Quoting StormTracker2K:
GFS is further north and east again. Miami watchout!!!



Yet the NHC nudges the cone even a little further west. Hopefully giving up on the GFS doesn't bite them in the ass again. I thought they would have left it right where it was but they're the experts so...
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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.
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Quoting SFLWeatherman:
Hey me two lol



You too :)
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Quoting ralphfurley:
Fort Lauderdale here. very cautious talk from weathermen on noon newscasts.
well at least they arent telling you folks your out of danger like my local radio mets
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Isaac has been amazingly consistent with his daytime and nighttime behaviors. Why has Isaac organized at night nicely and fallen into disarray every day? If it was size alone, I would expect his nighttime appearance to be far more similar to his daytime appearance.
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.
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I'll say 16N and assume the automated tracker over-corrected.

The visible imagery on 1km resolution has better quality and fewer optical illusions now that the Sun is directly over head.

1km visible loop

latest frame:

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Quoting interstatelover7165:
Correct, because of the forward speed of the storm pushes the heavy thunderstorms out to the right.


and because the velocity of the storm combines with the velocity of the wind field on the RHS.
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Quoting tkdaime:
I live in s florida I see people are starting yo put up there shutters I just moved here guess I don't know what I'm in for
Here too in SWF. I watched a neighbor put them up last night. Was gonna ask him if he would help me if needed. Not ready for that yet.
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I repeat:
Abrams was talking to the mayor of KW and they said they don't evacuate unless Cat 3 or higher.
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Quoting MississippiWx:
Final landfall is almost exactly the same on the 12z GFS. It just makes a little more interaction with the peninsula/S Florida than 6z.


Yes. Looking more and more like a total Florida state storm.....
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Flying in Isaac....

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Well. I am in the Tallahassee region and just called our roofer to shore up a small leak/some rotted wood on one part of the house on Sunday. Gonna trim the trees back this weekend. Never had to use them all these years (thankfully) but the pre-cut plywood for every window in the house is sitting in the garage. Good to go on batteries, gas, and other non-electric essentials.

Last thing, depending on the track on Sunday will be gassing up the cars and the Underwood Deviled Ham supply and bread........
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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.
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Fort Lauderdale here. very cautious talk from weathermen on noon newscasts.
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Quoting FLWeatherFreak91:
Starting to look like that worst scenario track for Tampa... just saying. People need to get less complacent around this city...



I really, really highly doubt we will see a worst case scenario for Tampa. Here is why. When you consider the type of steering that will be in place with Isaac, I do agree that track may shift closer to Tampa, however a hard right turn in the gulf is very unlikely with this scenario. For this storm to make a direct hit on the Tampa Bay area, it would likely have to first directly hit South Florida, which could still happen, but by then we would just have a butt load of rain and gusty winds. Nothing we aren't used to here in Tampa Bay, torrential rain, tropical storm force winds and tornadoes are common and are part of living here.

I do believe Isaac will take a turn into the eastern gulf, but I don't see how it could impact Tampa as a serious threat. Let's not start letting fear and hype get the best of us.
I'm not saying the worst case scenario is impossible, I mean, if Isaac were to rapidly deepen in a Katrina or Charley way, it could suddenly hook into Tampa. But lets remember the odds of that happening are extremely low. With that said, we must consider all possibility, but not get fearful or induce. Hype, the local MET Denis Phillips would agree with me right now, and that's why I follow his style, its sound science.


I'm not accusing you of hype, I know you are not that way, I'm really posting this for the sake of all bloggers, just be careful that other Floridians here don't think you are telling them that Tampa will be meeting it's doom in a few days.


At this point the storm could still even strike New Orleans. Now if the NHC has say a major hurricane consistently striking Tampa bay of this weekend, which I don't think will happen, then people need to start preparing for the big one, but even with that, people must still remain as calm and collective as they can.
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Monroe County Schools
Tropical Storm Information:

Due to the predicted weather conditions associated with Tropical Storm Isaac all Monroe County Schools, offices and facilities will be closed on Monday, August 27th. Identified shelter locations at: Key West High School, Switlik School and Coral Shores High School will open in accordance with directives from Monroe County Emergency Management. Note, Sugarloaf School has not been identified as a shelter location for this event.

Monroe County Emergency Management:

Tropical Storm Isaac, according to the National Hurricane Center’s 8 a.m. advisory now has sustained winds near the center at 50 mph. It is moving to the west at about 15 mph. According to the NHC latest track, the center of the storm should be over or near the Lower Keys late Sunday evening as a strong tropical storm.

Tropical storm-force winds are likely to begin affecting the Upper Keys Sunday morning, according to Chip Kasper, a forecaster at the Key West National Weather Service office.

A decision regarding visitor evacuations for the Keys is expected to be made later today, according to Irene Toner, director of Monroe County Emergency Management.

A full advisory is to be issued after that decision is made.


Shelters will be opened at 2:00 PM Saturday.
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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.