Isaac pounding Haiti and the Dominican Republic with torrential rains

By: Dr. Jeff Masters , 2:24 PM GMT on August 25, 2012

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Tropical Storm Isaac is pounding Haiti and the Dominican Republic with torrential rains that are causing extremely dangerous flooding and landslides. Isaac's center passed over Haiti's southwest peninsula early this morning, tracking about 50 miles west of the capital of Port-au-Prince. As the center pulled away to the northwest, Isaac's heaviest thunderstorms moved ashore over Hispaniola near sunrise, and are now dumping heavy rains with rainfall rates approaching one inch per hour, according to recent microwave satellite estimates. Barahona on the south coast of the Dominican Republic had received 5.14" of rain as of 8 am EDT this morning, and it is probable that some mountainous areas in Haiti and the Dominican Republic have already received up to 10" of rain from Isaac. These rains will continue though much of the day, and have the potential to cause high loss of life in Hispaniola.


Figure 1. A river north of Port-au-Prince, Haiti in flood due to rains from Isaac. Image from Amélie Baron via Twitter.

Latest observations
Isaac built a partial eyewall last night as the storm approached Haiti, but passage over the rough mountains of Haiti has destroyed the inner core, and the surface center of the storm is now fully exposed to view on satellite images. Radar out of Guantanamo Bay, Cuba shows no sign of an organized center, but does reveal some very intense thunderstorms affecting Eastern Cuba, Western Haiti, and nearby islands. Latest data from the Air Force Hurricane Hunters confirm that Isaac has weakened; during their penetration to obtain their 7:08 am EDT center fix, the aircraft reported top surface winds of 55 mph with their SFMR instrument, top flight-level winds at 5,000 feet of 68 mph, and a pressure rise of 3 mb, to 998 mb. Infrared and visible satellite loops show that Isaac remains a large and well-organized storm, though it lacks an inner core. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is still good to the north, but is lacking elsewhere. An impressive large multi-day satellite animation of Isaac is available from the Navy Research Lab.


Figure 2. Rainfall rates estimated by the NOAA F-17 polar orbiting satellite at 6:21 am EDT August 25, 2012. Rainfall rates of 1 inch per hour (orange colors) were occurring in a large area to the south of Hispaniola, and these heavy rains have now moved onshore. Image credit: Navy Research Laboratory.

Latest model runs for Isaac
The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs are similar in spread to the previous set of runs. Our two best models, the GFS and ECMWF, are virtually on top of each other, with a landfall location in the Florida Panhandle between Fort Walton Beach and Panama City. It is likely that the trough of low pressure pulling Isaac to the north will not be strong enough to pull Isaac all the way to the northeast and out to sea, and Isaac has the potential to drop torrential rains capable of causing serious flooding over the Southeast U.S. The latest 8-day precipitation forecast from the GFS model (Figure 3) calls for 10 - 15 inches of rain over portions of Georgia and South Carolina from Isaac. The ECMWF model, however, predicts that a ridge of high pressure will build in and force Isaac to the west after landfall, resulting in a slow motion across the Tennessee Valley into Arkansas by Friday. Arkansas is experiencing its worst drought in over 50 years, so the rains would be welcome there.


Figure 3. Predicted precipitation for the 8-day period from 2 am Saturday August 25 to 2 am Sunday September 2, from the 2 am EDT August 25 run of the GFS model. This model is predicting a wide swath of 5 - 10 inches of rain (orange colors) will affect portions of Cuba, Florida, the Bahamas, and the Southeast U.S. Image credit: NOAA/NCEP.

Intensity forecast for Isaac
Isaac survived passage over Hispaniola relatively intact. It's large size aided this, and this will also help it survive passage over Cuba today and Sunday. By the time Isaac pops off the coast of Cuba into the Florida Straits on Sunday, it will likely be a 50 mph tropical storm with a large, intact circulation. Isaac will be over very warm waters of 31°C (88°F) in the Florida Straits, wind shear will be light to moderate, and the upper-level wind pattern will feature an upper-level anticyclone over the storm, aiding its upper-level outflow. As I discussed in my previous post, Crossing Hispaniola and Cuba: a history, there have been five storms since 1900 with an intensity similar to Isaac, which crossed over both Haiti and Cuba, then emerged into the Florida Straits. These five storms strengthened by 5 - 20 mph in their first 24 hours after coming off the coast of Cuba. Given the relatively intact structure of Isaac so far, and the favorable conditions for intensification, I expect Isaac will intensify by 15 - 20 mph in 24 hours once the center moves off of the north coast of Cuba. If Isaac spends a full two days over water after passing the Florida Keys, it is possible that it will have enough time to develop a full eyewall and undergo rapid intensification into a Category 2 or 3 hurricane. The latest 06Z (2 am EDT) run of the GFDL model is calling for Isaac to intensify to Category 2 strength, then weaken to Category 1 at landfall in Mississippi on Tuesday. The 06Z HWRF run is calling for landfall in the Florida Panhandle near Fort Walton Beach as a borderline Category 2 or 3 hurricane. The 5 am EDT NHC wind probability forecast gave Isaac a 19% chance of becoming a Category 2 or stronger hurricane in the Gulf. I expect these odds are too low, and that Isaac has a 40% chance of becoming a Category 2 or stronger hurricane in the Northern Gulf of Mexico. I doubt the storm has much of a chance of hitting Category 4 or 5 status, though. While the surface waters in the Gulf of Mexico are very warm, near 30 - 31°C, the total heat content of these waters is unusually low for this time of year. We got lucky with the Gulf of Mexico Loop Current this summer, as it did not shed a big warm eddy during the height of hurricane season, like happened in 2005 (I discuss this in my Gulf of Mexico Loop Current Tutorial.) Without the type of super-high heat energy we had in 2005 in the Gulf of Mexico, Category 4 and 5 hurricanes in the Gulf of Mexico in 2012 will have difficulty forming.

Invest 97L off the coast of Africa
A tropical wave (Invest 97L) is located about 350 miles west-southwest of the Cape Verde Islands off the coast of Africa. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Monday morning. The 8 am EDT SHIPS model forecast predicts moderate shear for the next 5 days over 97L, so some development is possible if 97L can fend off the dry air to its north. None of the reliable models foresee that 97L will be a threat to the Lesser Antilles Islands. However, both the GFS and ECMWF models predict that a tropical wave that has not yet emerged from the coast of Africa may develop next week, and potentially take a more westward track towards the Lesser Antilles.

The Weather Channel's hurricane expert, Brian Norcross, is now writing a blog on wunderground.com. For those of you unfamiliar with his background, here's an excerpt from his first post, from last night:

"This evening 20 years ago the sun set on the horrendous first day after Hurricane Andrew. I was in downtown Miami at the studios of the NBC station. We knew that there was "total" destruction in South Dade County, but even that didn't describe it. Here's to the people that went through it... and held their families together in a situation that most people can't imagine."

Angela Fritz will have a new post here by 6 pm EDT. For the next few days, I plan to do the morning blog post, and Angela will be doing the late afternoon post.

Jeff Masters

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2421. Drakoen
Quoting WxLogic:
B. Center Fix Coordinates: 21°30'N 76°18'W (21.5N 76.3W)


Farther north and west of the NHC coordinates. Not surprising.
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Quoting Seflhurricane:
8pm



ok
Member Since: May 21, 2006 Posts: 5091 Comments: 114712
2419. WunderAlertBot (Admin)
JeffMasters has created a new entry.
2418. WxLogic
Given the warm shallow and semi deep shelf waters N of Cuba and Bahamas... I will not be surprised or RI to a 75 to 80 by 11PM.
Member Since: August 14, 2008 Posts: 4 Comments: 4928
I don't think the center is relocating, Isaac is a little too strong for that IMO... he's just a disorganized mess. He has to sort that out before he can strengthen more.
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2416. CCkid00
Quoting jazzygal:


I guess I'm just a little confused. Isn't this the Model that has all the data in it? Why is LA. out of the cone.
After reading the discussion at 5, I'm going to wait until Monday to see how everything sets ups.


Katrina was predicted to hit in the same place as Isaac is predicted to make final landfall, until 2 1/2 days before it hit. at that point, it was over 300 miles wrong. the turn happened later than they thought. so, until the turn, we in Louisiana are watching closely. could go either way??
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Quoting wpb:
weatherman on nbc6 in miami knows the storm is on one leg and can only get so far before it reaches the keys. also says rain could be the main issue for dade and broward with on and off gusts to 40 mph.
four stars for john.
others should be jailed for scaring air heads


Either you're a troll, or that guy needs to be fired.
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Quoting wolftribe2009:
I got a very tough question for anyone who might have the answer! When was the last time a storm skirted Cuba (Like Isaac) and then hit the Florida Panhandle as a Moderate to strong Hurricane? I can't think of one recently if there even ever was one; maybe if you can't find one then it is unlikely Isaac will do the same???


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2412. divdog
Quoting RTSplayer:




Look what the NHC discussion said about that new low...



THE INITIAL MOTION IS NOW 310/18. ISAAC IS CURRENTLY PART OF A
LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM COVERING THE NORTHWESTERN
CARIBBEAN SEA AND THE ADJACENT LAND AND OCEAN AREAS.

THIS LOW
PRESSURE AREA HAS A SECOND VORTICITY CENTER BETWEEN JAMAICA AND THE
CAYMAN ISLANDS...AND FOR THE NEXT 24-36 HR ISAAC AND THIS CENTER
WILL LIKELY ROTATE AROUND EACH OTHER
.

BASED ON THIS EXPECTATION...
THE FORECAST TRACK SHOWS ISAAC MOVING NORTHWESTWARD FOR 12 HR OR
SO...

FOLLOWED BY A TURN TOWARD THE WEST-NORTHWEST. IT IS POSSIBLE
THE STORM COULD MAKE A SHARPER TURN THAN FORECAST...AS THE UKMET IS
SHOWING AN ALMOST DUE WEST MOTION BETWEEN THE FLORIDA KEYS AND CUBA
NEAR THE 36 HR POINT
.


THE EARLY PART OF THE FORECAST TRACK IS
SHIFTED A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST...BUT STILL
LIES TO THE RIGHT OF THE CONSENSUS MODELS AND THE BULK OF THE
DYNAMICAL MODELS. AFTER 36 HR...ISAAC SHOULD BREAK FREE OF OR
ABSORB THE REST OF THE LOW
...WITH THE SUBTROPICAL RIDGE TO THE EAST
BECOMING THE DOMINANT STEERING INFLUENCE. THIS SHOULD ALLOW THE
STORM TO GRADUALLY TURN TOWARD THE NORTHWEST AND NORTH OVER THE
EASTERN AND NORTHERN GULF OF MEXICO...WITH AN EVENTUAL LANDFALL
ALONG THE NORTHERN GULF COAST IN 72-96 HR. WHERE THIS MIGHT OCCUR
IS STILL RATHER UNCERTAIN...WITH THE TRACK GUIDANCE SPREAD BETWEEN
SOUTHEASTERN LOUISIANA AND THE CENTRAL FLORIDA PANHANDLE. THIS PART
OF THE TRACK FORECAST LIES IN THE CENTER OF THE GUIDANCE ENVELOPE
NEAR THE CONSENSUS MODELS AND IS SIMILAR TO THE PREVIOUS FORECAST.



Other words, that is DEFINITELY another tropical low near Grand Cayman embedded in the monsoon, and it's going to pull Isaac west, and maybe even hard west, at some point around 36 hours.


Now they say it will all eventually be absorbed by Isaac, so
if that's the case, this is going to be one enormous storm by the time this merger/consolidation occurs.

Look how big of an area all of that convection and the monsoon trough covers!



and



Good explanation. Let's see how it plays out. Interesting days for sure. Keep up the good posts
Member Since: August 22, 2008 Posts: 0 Comments: 755
2411. Gorty
Quoting Civicane49:


Is that an eye?

And it looks like his structure is getting better organized. Am I right?
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18 hours out gfs
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Looks like it's pulling convection over the LLC
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Quoting Tazmanian:




looks like winds will go up too 65mph at 11pm
8pm
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Quoting HCW:


Ernesto called and said don't forget about me :)

Lol, we're on a roll this year.
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Quoting Michfan:
roduct: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 25th day of the month at 21:25Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 16
Observation Number: 07
A. Time of Center Fix: 25th day of the month at 21:14:30Z
B. Center Fix Coordinates: 21°30'N 76°18'W (21.5N 76.3W)
B. Center Fix Location: 104 miles (168 km) to the E (86°) from Camagüey, Cuba.
C. Minimum Height at Standard Level: 1,403m (4,603ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 59kts (~ 67.9mph)
E. Location of the Estimated Maximum Surface Wind: 90 nautical miles (104 statute miles) to the ESE (108°) of center fix
F. Maximum Flight Level Wind Inbound: From 139° at 56kts (From the SE at ~ 64.4mph)
G. Location of Maximum Flight Level Wind Inbound: 44 nautical miles (51 statute miles) to the E (85°) of center fix
H. Minimum Sea Level Pressure: 998mb (29.47 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,528m (5,013ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 19°C (66°F) at a pressure alt. of 1,522m (4,993ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 15°C (59°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.05 nautical miles
O. Meteorological Accuracy: 7 nautical miles
Remarks Section:
Maximum Flight Level Wind: 56kts (~ 64.4mph) in the east quadrant at 20:12:00Z
we may have a 70 MPH tropical storm at 11pm , so the indications are that it would very likely be a hurricane before reaching the florida keys
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Quoting sar2401:


Assume you're going to be hit by a cat 2 hurricane and plan accordingly. Until this maddening storm gets into the Gulf and establishes a vertically stacked and closed circulation, the models are going to shift back and forth with every run. If you need anything, get it now, since it will be a full blown panic if the Florida Panhandle landfall verfies.


rational and sensible post....What the hell is wrong with you?!?!?!?!?!
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Can someone post hwrf link please
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Quoting sar2401:


Assume you're going to be hit by a cat 2 hurricane and plan accordingly. Until this maddening storm gets into the Gulf and establishes a vertically stacked and closed circulation, the models are going to shift back and forth with every run. If you need anything, get it now, since it will be a full blown panic if the Florida Panhandle landfall verfies.


It is pretty well stacked if you asked me.

850 mb



700 mb



500 mb

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Quoting Michfan:
roduct: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 25th day of the month at 21:25Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 16
Observation Number: 07
A. Time of Center Fix: 25th day of the month at 21:14:30Z
B. Center Fix Coordinates: 21°30'N 76°18'W (21.5N 76.3W)
B. Center Fix Location: 104 miles (168 km) to the E (86°) from Camagüey, Cuba.
C. Minimum Height at Standard Level: 1,403m (4,603ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 59kts (~ 67.9mph)
E. Location of the Estimated Maximum Surface Wind: 90 nautical miles (104 statute miles) to the ESE (108°) of center fix
F. Maximum Flight Level Wind Inbound: From 139° at 56kts (From the SE at ~ 64.4mph)
G. Location of Maximum Flight Level Wind Inbound: 44 nautical miles (51 statute miles) to the E (85°) of center fix
H. Minimum Sea Level Pressure: 998mb (29.47 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,528m (5,013ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 19°C (66°F) at a pressure alt. of 1,522m (4,993ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 15°C (59°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.05 nautical miles
O. Meteorological Accuracy: 7 nautical miles
Remarks Section:
Maximum Flight Level Wind: 56kts (~ 64.4mph) in the east quadrant at 20:12:00Z




looks like winds will go up too 65mph at 11pm
Member Since: May 21, 2006 Posts: 5091 Comments: 114712
RTSplayer...thanks for post 2380...

This is really an interesting situation. If I understand what was said...Isaac will wobble more northward as it orbits the new system in the W Carib...then potentially veer a hard left when he absorbs the system....

I still think this W Carib tropical low has origins from split flow upper divergence between Isaac's ULAC and W Carib upper vortex...

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2400. CJ5
The convection to the NW is getting closer and closer to the center. We should know in an hour or so if it can pull it in and start wrapping something up.
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According to the NHS, its the Northern Gulf Coast . They didn't adjust the cone at all, but they will not move it until we get a firm hold. Watching the GFL closely now as it dropped the sharp hook back to the East late in the track...

WITH AN EVENTUAL LANDFALL
ALONG THE NORTHERN GULF COAST IN 72-96 HR.
WHERE THIS MIGHT OCCUR
IS STILL RATHER UNCERTAIN...WITH THE TRACK GUIDANCE SPREAD BETWEEN
SOUTHEASTERN LOUISIANA AND THE CENTRAL FLORIDA PANHANDLE.
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Quoting ProgressivePulse:


Does appear to be a developing LLC @ 22.3W 75.8N or minion circulation.


There is nothing at those coordinates, and that is confirmed by recon as they just found the center a few minutes ago. The center is right where it should be on satellite.

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Quoting tropicfreak:


Keep it coming... doing a great job entertaining me!


HEY I AIN'T ENTERTAINING ANYONE

I am be straight up all I am saying is what if that is all
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Quoting Drakoen:
They are finding southwest winds north of the NHC coordinates... what a mess.


Wouldn't that indicate that the circulation center is north of the NHC coordinates?
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2395. HCW
Quoting MAweatherboy1:
Isaac has to be one of the ugliest systems of all time, lol.



Ernesto called and said don't forget about me :)
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2394. Michfan
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 25th day of the month at 21:25Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 16
Observation Number: 07
A. Time of Center Fix: 25th day of the month at 21:14:30Z
B. Center Fix Coordinates: 2130'N 7618'W (21.5N 76.3W)
B. Center Fix Location: 104 miles (168 km) to the E (86) from Camagey, Cuba.
C. Minimum Height at Standard Level: 1,403m (4,603ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 59kts (~ 67.9mph)
E. Location of the Estimated Maximum Surface Wind: 90 nautical miles (104 statute miles) to the ESE (108) of center fix
F. Maximum Flight Level Wind Inbound: From 139 at 56kts (From the SE at ~ 64.4mph)
G. Location of Maximum Flight Level Wind Inbound: 44 nautical miles (51 statute miles) to the E (85) of center fix
H. Minimum Sea Level Pressure: 998mb (29.47 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17C (63F) at a pressure alt. of 1,528m (5,013ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 19C (66F) at a pressure alt. of 1,522m (4,993ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 15C (59F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.05 nautical miles
O. Meteorological Accuracy: 7 nautical miles
Remarks Section:
Maximum Flight Level Wind: 56kts (~ 64.4mph) in the east quadrant at 20:12:00Z
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2393. wpb
weatherman on nbc6 in miami knows the storm is on one leg and can only get so far before it reaches the keys. also says rain could be the main issue for dade and broward with on and off gusts to 40 mph.
four stars for john.
others should be jailed for scaring air heads
Member Since: May 28, 2011 Posts: 0 Comments: 572
they went with the 67.9mph surface winds in the vortex
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2390. WxLogic
B. Center Fix Coordinates: 21°30'N 76°18'W (21.5N 76.3W)
Member Since: August 14, 2008 Posts: 4 Comments: 4928
Isaac has to be one of the ugliest systems of all time, lol.

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Quoting ProgressivePulse:


Does appear to be a developing LLC @ 22.3W 75.8N or minion circulation.
noticing that very near the new convection firing if that is confirmed that is much farther to the NE than the current position
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Quoting Hurricanes101:


looks like they found the center, .2N and .2W of the 5pm

21:14:00Z 21.483N 76.267W 842.9 mb
(~ 24.89 inHg) 1,474 meters
(~ 4,836 feet) 997.9 mb
(~ 29.47 inHg) - From 57� at 0 knots
(From the ENE at ~ 0.0 mph)


Missed it by just a tad.

Time: 21:14:30Z
Coordinates: 21.5N 76.3W
Acft. Static Air Press: 843.0 mb (~ 24.89 inHg)
Acft. Geopotential Hgt: 1,472 meters (~ 4,829 feet)
Extrap. Sfc. Press: 997.7 mb (~ 29.46 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 72° at 3 knots (From the ENE at ~ 3.4 mph)
Air Temp: 18.6°C (~ 65.5°F)
Dew Pt: 15.5°C (~ 59.9°F)
Peak (10s) Flt. Lvl. Wind: 4 knots (~ 4.6 mph)
SFMR Peak (10s) Sfc. Wind: -
SFMR Rain Rate: -
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2386. sar2401
Quoting mfcmom:
Any guesses on Panama City impact yet, looks to have pulled a little west? Thank you.


Assume you're going to be hit by a cat 2 hurricane and plan accordingly. Until this maddening storm gets into the Gulf and establishes a vertically stacked and closed circulation, the models are going to shift back and forth with every run. If you need anything, get it now, since it will be a full blown panic if the Florida Panhandle landfall verfies.
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Suggestion of two systems possibly with one west of Isaac? What??? What a strange couple days with Isaac. Great that the NHC still giving Isaac less than a ten percent chance of reaching major status. I'll check out 2340, thanks NCHurricane2009.
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Quoting spathy:
Well I should have nothing to worry about. Or they missed a spot (Lee County Fl)Fort Myers.

LOL

Wondering where you've been the past couple days! I for one just happy we're not in the cone anymore..not good for others, stay safe all
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Quoting Drakoen:
They are finding southwest winds north of the NHC coordinates... what a mess.
What might that mean Drak?
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2381. LargoFl
Quoting Hurricanes101:


yea they have us getting gusts to 60mph in st petersburg
and a possible 5-7 ft storm surge depending
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Quoting NCHurricane2009:


I still vote for a slight rightward bias in track...because of this system you point out. I find it interesting this new system west of Isaac has been producing a very persistent burst of clouds in the Florida Straits since 12 hrs ago...pretty cool....

At the upper-levels...this system is getting split in half...into one ULL in the W Carib...another ULL over the Carolinas...the split driven by Isaac's massive ULAC. Mabye ULL over the Carolinas is too far north to influence Isaac's track...but the W Carib ULL may help continue the more poleward Isaac track.

Plus Isaac is now in the east side of a broad surface low pressure field extending into the W Carib. This new surface low pressure field has been generated by split flow upper divergence between Isaac's ULAC...W Carib ULL...and Carolinas ULL. Cyclonic flow on the east side of the surface low pressure field may also help a more poleward track for Isaac....




Look what the NHC discussion said about that new low...



THE INITIAL MOTION IS NOW 310/18. ISAAC IS CURRENTLY PART OF A
LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM COVERING THE NORTHWESTERN
CARIBBEAN SEA AND THE ADJACENT LAND AND OCEAN AREAS.

THIS LOW
PRESSURE AREA HAS A SECOND VORTICITY CENTER BETWEEN JAMAICA AND THE
CAYMAN ISLANDS...AND FOR THE NEXT 24-36 HR ISAAC AND THIS CENTER
WILL LIKELY ROTATE AROUND EACH OTHER
.

BASED ON THIS EXPECTATION...
THE FORECAST TRACK SHOWS ISAAC MOVING NORTHWESTWARD FOR 12 HR OR
SO...

FOLLOWED BY A TURN TOWARD THE WEST-NORTHWEST. IT IS POSSIBLE
THE STORM COULD MAKE A SHARPER TURN THAN FORECAST...AS THE UKMET IS
SHOWING AN ALMOST DUE WEST MOTION BETWEEN THE FLORIDA KEYS AND CUBA
NEAR THE 36 HR POINT
.


THE EARLY PART OF THE FORECAST TRACK IS
SHIFTED A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST...BUT STILL
LIES TO THE RIGHT OF THE CONSENSUS MODELS AND THE BULK OF THE
DYNAMICAL MODELS. AFTER 36 HR...ISAAC SHOULD BREAK FREE OF OR
ABSORB THE REST OF THE LOW
...WITH THE SUBTROPICAL RIDGE TO THE EAST
BECOMING THE DOMINANT STEERING INFLUENCE. THIS SHOULD ALLOW THE
STORM TO GRADUALLY TURN TOWARD THE NORTHWEST AND NORTH OVER THE
EASTERN AND NORTHERN GULF OF MEXICO...WITH AN EVENTUAL LANDFALL
ALONG THE NORTHERN GULF COAST IN 72-96 HR. WHERE THIS MIGHT OCCUR
IS STILL RATHER UNCERTAIN...WITH THE TRACK GUIDANCE SPREAD BETWEEN
SOUTHEASTERN LOUISIANA AND THE CENTRAL FLORIDA PANHANDLE. THIS PART
OF THE TRACK FORECAST LIES IN THE CENTER OF THE GUIDANCE ENVELOPE
NEAR THE CONSENSUS MODELS AND IS SIMILAR TO THE PREVIOUS FORECAST.



Other words, that is DEFINITELY another tropical low near Grand Cayman embedded in the monsoon, and it's going to pull Isaac west, and maybe even hard west, at some point around 36 hours.


Now they say it will all eventually be absorbed by Isaac, so if that's the case, this is going to be one enormous storm by the time this merger/consolidation occurs.

Look how big of an area all of that convection and the monsoon trough covers!



and

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Quoting Hurricanes101:


looks like they found the center, .2N and .2W of the 5pm


Pressure still 997
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RGB show Isaac is really starting to organize the core is off the cuban coast about 20-30 miles off shore i would say
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2377. WxLogic
Quoting Jedkins01:
Local NWS notes that the Tampa Bay area will be in a strong pressure gradient between Isaac and the high, therefore winds will be quite robust in the area even if it passes a decent distance to our west.


Should be even stronger if it decides to go above Cat 1 before it gets to Key West.
Member Since: August 14, 2008 Posts: 4 Comments: 4928
Quoting ProgressivePulse:


Does appear to be a developing LLC @ 22.3W 75.8N or minion circulation.
That's where the HWRF had it.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
2375. airmet3
Quoting milo617:
Meanwhile in the pacific....




Kadena Air Base is in the path and will see passage in about 12 hours. The ICAO code is RODN if you want to track the observations.
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It is going to take atleast 8 hours for the surface center to reorganize.. Chill out guys.. It did just get shredded by mountains..
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Quoting TropicalAnalystwx13:

You're over-analyzing.

But Isaac is more complex than it seems...at least to me anyway :)
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Quoting Jedkins01:
Local NWS notes that the Tampa Bay area will be in a strong pressure gradient between Isaac and the high, therefore winds will be quite robust in the area even if it passes a decent distance to our west.


yea they have us getting gusts to 60mph in st petersburg
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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.