Florida Weather Update

There is a lot to cover tonight on the blog as Tropical Storm Isaac is about 75 miles southwest of Key West.

The 8 pm EDT advisory has Isaac 24.2N 82.9W, and moving WNW (285 degrees) at 14 mph. Max winds have jumped a bit to 65 mph with a minimum central pressure of 993 mb. The storm has been doing some interesting things for the last few hours. The tropical storm has increased thunderstorm activity around the center of circulation – mainly around the western side – based on satellite imagery. It gives the appearance that Isaac is beginning to get its act together. Regardless, latest recon data doesn’t necessarily show any intensification of the storm.

Source: NOAA

The radar imagery has given the appearance that Isaac was moving more northerly than northwest. But it’s not happening as the 11 pm EDT advisory shows Isaac moving west-northwest at 14 mph.

The thing that will keep Isaac tempered is the drier air off to the south and east of the storm. A lot of the convection seems to be on the western side, but the counterclockwise flow is bringing more drier air around it. Also, there is a lack of good convection on the southern half of the storm – the convection is asymmetric at this point. The dry air is also being pulled in by an upper-level low just to the west of Isaac.

The future track of Isaac remains to be very uncertain as the guidance models continue to jump around. There are some factors at play. One is the ridge off to the east of Isaac and the second is the aforementioned  upper-level low to the west. The low is expected to move westward away from Isaac (see the GFS’ scenario below). This can do two things: 1) It will help cut the dry air intrusion in Isaac and 2) help steer Isaac northwest.

Here’s where things can get tricky: Most of the models – except for the Sunday morning European – have taken a shift to the west to Louisiana. With all of the shifting that has taken place, my confidence in the guidance models remains low. Everyone on the gulf coast needs to keep an eye on this. Floridians living in the panhandle should not breathe a sigh of relief just yet.

The intensity is also uncertain. If this upper low moves away – and the models expect it – Isaac has a chance to gain strength. The NHC is thinking category 2 strength (96-110 mph) before landfall. I see it as a reasonable forecast. But I’ve seen intensity surprises before (think of Hurricane Charley in 2004). The gulf waters continue to be in the mid 80s – even higher in some spots, so there is a possibility of further intensification. One good glimmer of hope is that the depth of the warm water isn’t as great as it has been in the past, so the fuel isn’t as abundant. Still, whether it’s a cat 2, or 3, or 4, or, hell, even a 1, people still need to prepare for the possibility of storm surge, flooding, strong winds, and a threat of a tornado or two inland.

Hurricane warnings are in effect on the gulf coast from east of Morgan City, La. east to Destin, Fla. People living in those areas should heed any evacuation orders from local officials. The time to prepare is now.

Expect the next full update to be sometime Monday evening. Keep checking our Twitter and Facebook feeds for the latest info and brief analysis on Isaac.

As I thought it would, Tropical Storm Isaac has weakened a bit this morning as it approached Cuba. Winds have dipped to 60 mph and the central pressure has risen to 998 mb as of the 11 am EDT advisory. The storm has lost a lot of its deep convection on the northwestern side. The interaction with the land is likely the culprit. Isaac continues to move to the northwest at 17 mph (a tad faster).

Source: NOAA

The area of convection over southern Florida and north of central Cuba is associated with a trough of low pressure in the upper levels. This trough will also help guide Isaac to the northwest over time.

In terms of intensification, there are some uncertainties – in my opinion – to the NHC’s intensity forecast. The NHC is saying that Isaac could be a hurricane when it reaches the Florida Keys on Sunday. Even though the models are in agreement that the center of circulation will be over the water off the northern Cuban coast, there are some factors that could hamper intensification.

1) Even though Isaac will be over water, the counterclockwise flow can pull in some drier air off the islands and the mountains.

2) The counterclockwise flow could cause some upwelling on the northern coast, pull of cooler water, and, therefore, leave less fuel to aid in redevelopment.

I think it will more likely be a strong tropical storm when it makes a direct hit on the Florida Keys on Sunday. It could still strengthen to a low category 1, but I think it’s not as likely. But the big concern is what would happen when the tropical storm enters the Gulf of Mexico. The water temperatures in the gulf are pretty much like bath water, and intensification is a good possibility. But there is no way to be certain as tropical cyclone intensification forecasting is still a challenge in the meteorological profession.

As for a final landfall location, the models continue to wave back and forth from east to west, and west to east. Regardless of an exact landfall location, it is very certain that the Florida panhandle will feel the effects of Isaac and precautions need to be taken.

As for south Florida, heavy rain will be a good possibility today as the trough helps develop showers and storms. Conditions will continue to deteriorate tonight and into tomorrow as the bands from Isaac move into the Keys and into southern Florida. Hurricane warnings are in effect for the Keys and portions of southwestern Florida (see map below with other advisories).

Source: National Hurricane Center

Visitors in Key West have been asked to leave if they have the means to do so. Reports from Twitter say that traffic on US Highway 1 – the only way in and out of the Keys – is already experiencing heavy traffic. If you are asked to leave by local emergency management, please do so.

Keep tabs on our Facebook and Twitter feeds for the latest. Expect a full update later this evening.

Isaac is growing up. *Snif* The last few days have been tough as Tropical Storm Isaac has been battling dry air intrusion and shear for the last few days. I noticed on satellite imagery late Friday morning that the storm was beginning to show convection wrapping around the center of circulation. As the day wore on, it really began to show signs of organization. Since then, the minimum central pressure has fallen and it began to make a northwesterly turn and slowed down a bit in forward speed. Here is the latest 2 am EDT information on Isaac from the NHC…

LOCATION…18.0N 72.8W
ABOUT 55 MI SW OF PORT AU PRINCE HAITI
ABOUT 220 MI SE OF GUANTANAMO CUBA
MAXIMUM SUSTAINED WINDS…70 MPH
PRESENT MOVEMENT…NW OR 310 DEGREES AT 13 MPH
MINIMUM CENTRAL PRESSURE…990 MB…29.23 INCHES

It is getting very close to Haiti early this morning as it’s 55 miles from Port Au Prince. Flooding will be the greatest concern as Isaac continues to move towards the island of Hispaniola. The storm is expected to continue a northwest movement and begin to directly impact Cuba today. Isaac could lose some strength due to the interaction with the land.

Source: NOAA

The circulation is looking much better and convection, as I mentioned, is wrapping around the center. Convection doesn’t look as tall, however. It is likely that some drier air is being pulled from the Cuba and Hispaniola as the TC pulls in surrounding air into the center of circulation. It may not intensify as fast and have very high thunderstorm tops. You can see on the image above that the highest cloudtops are on the southern half of the storm over the Caribbean Sea.

I am confident that effects from Isaac will be felt in the state of Florida. The question is how much? It depends on how far out in the gulf the storm travels, and if it can hold together from the expected land interactions and regain intensity in the warm gulf waters.

Hurricane watches have been put in place in Florida…

FLORIDA KEYS INCLUDING THE DRY TORTUGAS
FLORIDA BAY
THE FLORIDA EAST COAST FROM OCEAN REEF SOUTHWARD
THE FLORIDA WEST COAST FROM BONITA BEACH SOUTHWARD

This means that hurricane conditions are possible within 36 hours. Tropical storm warnings are also in effect for parts of south Florida. These watches and warnings may change during the day Saturday.

Floridians should initiate their hurricane preparedness procedures. For more info on what to do, check out ready.gov. Expect the next full update this afternoon.

The latest info on Tropical Storm Isaac (from 11 pm EDT) hints at some strengthening. I am careful to say “strengthening” at the moment because Isaac, well, doesn’t look that sharp in terms of  convection wrapping around the center. Shear to the northeast of the storm may still be giving Isaac more trouble than a Yankee fan at a Red Sox game. Another possibility that occurred to me this evening is, since the span of Isaac is so large, that the weak tropical storm may be pulling some drier air from Venezuela. Thanks, Chavez. Regardless, the storm has been struggling for the last day or two to get its act together. But the latest infrared imagery is showing some relatively high cloudtops roughly around 15° N 70.5° W. Still, the center of circulation is located to the northeast of the highest cloudtops (16.7° N 68.7° W). If Isaac wants to be a big boy…storm…it needs to get some convection wrapped around the center of circulation.

Source: NOAA

The minimun central pressure has fallen to 1001 mb and the winds have jumped slightly to 45 mph. The movement is more west-northwest (290 degrees) at 18 mph.

The NHC has, once again, moved the cone of error more west, and has the center of the error cone over coastal Mississippi and Alabama. The models (shown below) are mainly thinking of the Florida panhandle at this point. Disclaimer: This could change. NOAA had the G-IV jets over the Bahamas to gather data in the area of the ridge to the north of Isaac. This data will be (or probably already has been) placed in the guidance models and we should have a more accurate assessment of what path Isaac could take. It will be interesting to see what the models say Friday morning.

At the rate Isaac is not intensifying, I feel it might go a tad more west. But I am still not confident in making decision yet on its final destination. We’ll see if this slight strengthening is just a phase. I feel we will know more Friday or Saturday.

Floridians are not off the hook yet. Regardless of where the center of the storm would make landfall, this storm is large and its effects will be felt at distances far from the tropical cyclone. Those on the gulf coast should make sure any hurricane plans they have are on standby.

Tonight, Tropical Storm Isaac hasn’t changed too much since last night’s update in terms of strength. The storm has been impacted by dry air intrusion and some shear to the northeast of Isaac.

As of 11 pm EDT, Isaac was 270 miles southeast of Puerto Rico and moving quickly west at 20 mph. The central pressure has dropped a bit to 1003 mb, with the winds at 45 mph.

It didn’t look too impressive on satellite imagery Wednesday evening, but the latest infrared imagery shows better organization. I wouldn’t be surprised if the center of circulation will be shifted in forthcoming advisories as the storm continues to “find itself” and organize.

Source: NOAA

Here is what the latest recon found…

HOWEVER…DROPSONDE DATA FROM A NOAA AIRCRAFT CURRENTLY INVESTIGATING THE STORM SUGGEST THAT THE CENTER HAS PROBABLY BECOME A LITTLE BETTER DEFINED AND THAT THE MINIMUM PRESSURE HAS DROPPED A BIT.  THERE HAS ALSO BEEN AN INCREASE IN COLD-TOPPED CONVECTION NEAR AND OVER THE ESTIMATED CENTER SO THE CURRENT INTENSITY IS HELD AT 40 KT.  ISAAC HAS DEVELOPED AN IMPRESSIVE UPPER-LEVEL OUTFLOW PATTERN AND DYNAMICAL GUIDANCE SHOWS THAT THE VERTICAL SHEAR SHOULD REMAIN WEAK DURING THE NEXT SEVERAL DAYS.

If Isaac does impact the islands, it has a chance of deflating in strength due to the land and mountainous terrain. Will it brush the islands, or just go completely over them? If the latter occurs, will it survive? Will there be anything? This is why the intensity forecast is highly uncertain at this point.

Since last night, the models have shifted a little more left (west) to the far eastern Gulf of Mexico and western Florida. In fact, this morning’s European model run had the storm eyeing Louisiana. But will all the new data from the recon flights alter the model’s trajectory of Isaac?

It’s important to keep in mind that this tropical storm is a LARGE system. Even if the center of circulation misses a specific location, say, Miami, by 100 miles, the metro area will still feel the effects of Isaac.

Until all of the data is ingested by the guidance models, my forecast in regards to track remains low in confidence. With all of the land and mountains that Isaac may interact with, my intensity forecast is also in low confidence . I think we will have a better idea of what could happen Thursday or Friday. I urge people in Florida not to panic, but to be vigilant. Keep checking back for the latest information on Isaac. Make sure you have your hurricane plans on standby.

The rain and severe weather associated with now Tropical Depression Debby is almost over. Satellite and radar imagery hint that her center of circulation has made it back into the Atlantic. Debby appears to be offshore of Flagler County at the moment and continues to move east-northeast at 10 mph. The Melbourne radar is showing some light precip in parts of east central Florida including Titusville, Kissimmee, Orlando. There’s another light band of precip stretching from near Punta Gorda northeastward to Fort Pierce. All of this is moving east and northeast.

As Debby moves away from the Florida coast, there will be a less of an influence. This is good news as Florida really doesn’t need any more rain.

Panhandle: Partly cloudy with a slim chance of a shower. Highs in the low 90s inland and upper 80s along the coast.

North Florida: Partly cloudy with a slim chance of a shower. Highs near 90 inland and upper 80s along the east coast.

Central Florida: Mostly cloudy with a chance of a shower – greater rain chances towards the east. Highs in the upper 80s, but it could get close to the 90 mark in a few spots.

South Florida: Partly cloudy with a chance of showers and a thunderstorm. Highs in the upper 80s along the coasts to lower 90s inland.