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 galvestonhurricane:


wunderkidcayman better pay attention to the XTRP model...


lol
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1510. Grothar
Quoting StormTracker2K:


Gro the experts said to throw it out. Idiots!


Nobody listens to old people anymore. :)

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Time: 19:52:00Z
Coordinates: 16.7833N 71.6W
Acft. Static Air Press: 842.9 mb (~ 24.89 inHg)
Acft. Geopotential Hgt: 1,452 meters (~ 4,764 feet)
Extrap. Sfc. Press: 995.5 mb (~ 29.40 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 239° at 13 knots (From the WSW at ~ 14.9 mph)
Air Temp: 18.0°C* (~ 64.4°F*)
Dew Pt: 18.0°C* (~ 64.4°F*)
Peak (10s) Flt. Lvl. Wind: 15 knots (~ 17.2 mph)
SFMR Peak (10s) Sfc. Wind: 24 knots (~ 27.6 mph)
SFMR Rain Rate: 6 mm/hr (~ 0.24 in/hr)
(*) Denotes suspect data
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Quoting StormTracker2K:
This is the worst case scenario for FL as the NHC again follows the Euro while a storm comes to FL and people get complacent as the local mets say we are in the clear. Very Very bad reasoning here.

NHC will have no choice but to adjust the track to hug the SW FL coast either at 5pm or 11pm.




Chill man, the NHC isn't following the euro, back with Debby the euro had a consensus backing it and the GFS was the outlier. Debby was a very interesting situation where their was almost an equal chance of Debby going either way, it was only reasonable to choose the model consensus. Here the NHC is choosing the consensus, they aren't following the euro and have already shifted their track to the right twice today. It may shift slightly more to the right but nothing drastic which is again reasonable. Think about it professionally, it makes sense they do things the way they do. They try their best to be fair and balanced unlike the media, politics, or many in this blog. Because they have no agenda at stake, they are their to inform people the best they can. Yes they get it wrong sometimes and i don't always agree with them either, but they do a great job.
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1507. FOREX
Quoting tornadolarkin:
The fact that Isaac still hasn't organized is blowing my mind.


It is a lot better organized than 72 hours ago. Looks like some more slow strengthening then some weakening over Cuba, then stronger again after re-emerging into the Gulf.
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Quoting GTcooliebai:
What it looks like based on those models is the High builds in and the trough is enough to erode the Northwestern Flank of the High and create a weakness pulling it Northeast. The Euro is by itself and has the storm after it makes landfall going Northwest.
The Euro did the same thing with Debbie had it going west and the GFS was right all the time with Debbie
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Huh, interesting. Consensus now saying it will only briefly make landfall in Cuba now.. greatly reducing the time it will have to spend over Cuba, NHC is probably going to shift slightly north.
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1504. FLSurf
Quoting CloudGatherer:
...and there we go. The hunter has curved all the way around to a northwestern heading, and is commencing a second pass through the center of the circulation. Much weaker winds in this southeastern quadrant - none on the surface that would justify even a tropical storm. Pressure down to 999MB, and temps steady at 17C. The next message should tell us just how fast Isaac is strengthening now.



DO YOU HAVE A LINK TO THESE "MESSAGES"
?
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Quoting HCW:
that's pretty good agreement for this far out



wunderkidcayman better pay attention to the XTRP model...
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Quoting Grothar:
So should I stop posting this or what?



Yes Gro! You know that was thrown out because it was wrong :-b
Member Since: August 19, 2005 Posts: 5 Comments: 5401
Quoting gustavcane:
THE 06Z/12Z GFS AND 12Z CANADIAN SOLUTIONS HAD TO
BE THROWN OUT BY DEFAULT.

That may be why Jim Cantore 
is on the central gulf coast and not in or near florida.

jim cantore is on TWC right now
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Quoting presslord:


that's kind like being "the prettiest girl in Accounting"


That's a rather low blow eh?

Rick Nabb was TWC expert last year, and now he's director of the NHC.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting jrweatherman:
Repeat after me:
It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.


Actually, the southern edge of the NHC cone, which is much like the EURO, takes the center of a very large cyclone very close to Cayman Brac and Little Cayman. Although they wouldn't get the dirty side of Isaac, if the storm takes the southern edge of the 3-day cone track - which is certainly in the realm of possibility according to the NHC - the "Caymans" will get pounded. So ease up dude.
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1498. FOREX
Quoting leelee75k:
The Weather Channel tropical desk is on the Gulf Coast? Cuz I'm watching Cantore in studio on tv now. LOL!!


lol. They must be in the truck, driving back and forth.
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The fact that Isaac still hasn't organized is blowing my mind.
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1496. Grothar
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Quoting Grothar:
So should I stop posting this or what?



Gro the experts said to throw it out. Idiots!
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Quoting MelbourneTom:


Link please.


Hey there MelbourneTom... right here in your neck of the woods :)
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Quoting RAMPAGE127:
Cantore is still in ATL, nice try wishcaster's.


he wouldn't be going down there yet anyways. Its too early. Give him to this weekend.
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Quoting FOREX:


The local METS here in PCB disagree, but who knows. As of 15 minutes ago WJHG METS still think it will go well east of PC Beach. I'll be happy when I know for sure so I can go to the bank and start preparing.


It might be too late by then. Anyone on the projected path should be preparing right now!
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Quoting GTcooliebai:
What it looks like based on those models is the High builds in and the trough is enough to erode the Nortwestern Flank of the High and create a weakness pulling in Northeast. The Euro is by itself and has the storm after it makes landfall going Northwest.
Quoting Jedkins01:
The NHC isn't going to swing it's forecast track way east just because the GFS has shifted well east. They are discounting it because they plan to wait and see how additional runs from the model turn out, as well as to see how runs from the other models turn out. The overall consensus has shifted a little further to the east this afternoon, so I expect the NHC to adjust it a bit more east at the 5 PM advisory or maybe by tonight if the trend continues. They do that for a reason, because if they flip flopped their track back and forth all the time that makes them unrealistic and unreliable. But of course contentious individuals never stop to think about that.


Yeah just like you said I would be wrong with Debby right? THe NHC is the furthest left of all the models because they are using the Euro's reasoning. Look at the consensus along the SW FL coast.

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1490. Grothar
So should I stop posting this or what?

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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 24th day of the month at 19:05Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 12
Observation Number: 02
A. Time of Center Fix: 24th day of the month at 18:43:50Z
B. Center Fix Coordinates: 16°48'N 71°31'W (16.8N 71.5167W)
B. Center Fix Location: 132 miles (212 km) to the SSE (156°) from Port-au-Prince, Haiti.
C. Minimum Height at Standard Level: 1,381m (4,531ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)
E. Location of the Estimated Maximum Surface Wind: 49 nautical miles (56 statute miles) to the ENE/E (79°) of center fix
F. Maximum Flight Level Wind Inbound: From 155° at 70kts (From the SSE at ~ 80.6mph)
G. Location of Maximum Flight Level Wind Inbound: 68 nautical miles (78 statute miles) to the ENE (75°) of center fix
H. Minimum Sea Level Pressure: 995mb (29.38 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 14°C (57°F) at a pressure alt. of 1,524m (5,000ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 1,525m (5,003ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 16°C (61°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 Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 4 nautical miles
Remarks Section:
Maximum Flight Level Wind: 70kts (~ 80.6mph) in the east quadrant at 18:21:30


5 Pm Advisory:
65 Mph
995 MB. Unless Recon finds different pressure on next center fix.
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look at the inflow bands to the south of Isaac's center. WOW! That is all I have to say. Now I have to wonder if the wrap up of thunderstorms around the center might help create the first eyewall signs that we have yet to see.

Link
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1487. A4Guy
I think it should be mandatory to have your location included as part of your screen name. It would explain a LOT - especially with the home-drawn forecasts. I am sure 90% of them take the storm to the poster's doorstep. Would also expose those screaming "it's going West...not Northwest" - it will be no surprise that the direction being advocated similarly takes the storm to their house (or on a path in their general direction).
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Quoting RTSplayer:


Wait, what happened that I missed?

I was eating...


Link please.
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Quoting wunderkidcayman:


that is very true Taz it is getting quite annoying I never even said cayman and this guy has gone crazy because he his hearing things and seeing thing


Well...I know you never SAID that.

It just came across that way the way you were emphasizing scenarios and wanting to see things with every storm that would bring it to the Caymans.
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...and there we go. The hunter has curved all the way around to a northwestern heading, and is commencing a second pass through the center of the circulation. Much weaker winds in this southeastern quadrant - none on the surface that would justify even a tropical storm. Pressure down to 999MB, and temps steady at 17C. The next message should tell us just how fast Isaac is strengthening now.
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Quoting tropicfreak:


That has been my thinking all along.

same here...
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Floracastin
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Quoting MAweatherboy1:
The 12z GFDL solution is reasonable IMO. Clips S FL first:



Then brings it through the Gulf to the panhandle:



Yeah I think the GFDL is pretty much the consensus between the far right and far left models right now.
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Quoting wunderkidcayman:


that is very true Taz it is getting quite annoying I never even said cayman and this guy has gone crazy because he his hearing things and seeing thing



yep so ture
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Cantore is still in ATL, nice try wishcaster's.
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1478. FOREX
Quoting MAweatherboy1:

I don't think he has an eye. Recon hasn't reported one. I think any eye like feature is just dry air.

Cantore has been cloned. He is in Mobile and Atlanta. Turn on TWC.
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The Weather Channel tropical desk is on the Gulf Coast? Cuz I'm watching Cantore in studio on tv now. LOL!!
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Quoting gustavcane:
THE 06Z/12Z GFS AND 12Z CANADIAN SOLUTIONS HAD TO
BE THROWN OUT BY DEFAULT.
 

there you have it folks.



Wait, what happened that I missed?

I was eating...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting Tazmanian:




will you this STOP WITH THAT its getinng annoying


that is very true Taz it is getting quite annoying I never even said cayman and this guy has gone crazy because he his hearing things and seeing thing
Member Since: June 13, 2009 Posts: 2 Comments: 12019
Quoting Hurricane1956:
It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.



will you this STOP WITH THAT its getinng annoying


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Quoting WxGeekVA:
inb4 the eye is fully wrapped now

I don't think he has an eye. Recon hasn't reported one. I think any eye like feature is just dry air.

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Quoting MAweatherboy1:
The 12z GFDL solution is reasonable IMO. Clips S FL first:



Then brings it through the Gulf to the panhandle:



That has been my thinking all along.
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Quoting CocoaLove:


Where are you? Miami Lakes area here.
I'm in Key Biscayne, watching very closely as a landfall on the actual SFLA mainland is becoming much more likely compared to a Keys landfall.
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Quoting StormTracker2K:
This is the worst case scenario for FL as the NHC again follows the Euro while a storm comes to FL and people get complacent as the local mets say we are in the clear. Very Very bad reasoning here.

NHC will have no choice but to adjust the track to hug the SW FL coast either at 5pm or 11pm.


What it looks like based on those models is the High builds in and the trough is enough to erode the Northwestern Flank of the High and create a weakness pulling it Northeast. The Euro is by itself and has the storm after it makes landfall going Northwest.
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1469. jambev
1432 Yoda1550

Brilliant! The funniest I have seen in a while.
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1467. Seastep
Quoting WxGeekVA:
inb4 the eye is fully wrapped now


What is inb4?
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The NHC isn't going to swing it's forecast track way east just because the GFS has shifted well east. They are discounting it because they plan to wait and see how additional runs from the model turn out, as well as to see how runs from the other models turn out. The overall consensus has shifted a little further to the east this afternoon, so I expect the NHC to adjust it a bit more east at the 5 PM advisory or maybe by tonight if the trend continues. They do that for a reason, because if they flip flopped their track back and forth all the time that makes them unrealistic and unreliable. But of course contentious individuals never stop to think about that.
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HH making another center run...
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inb4 the eye is fully wrapped now
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Quoting tropicfreak:


Wunderkid.... need I say more?


To be honest I never read where he said that about Isaac! BTW , laugh at him, criticize him, make fun of him, but he has been fairly accurate with the movement of Isaac so far, nuff said!
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Quoting JLPR2:
With El Nino weaker, the GFS is showing an active start to September, with Kirk, Leslie, Michael and Nadine.



If that does materialize this blog will go haywire, 4 storms at the same time?
Overload... xD


....last peak 2nd week Aug but now going in the tank....SOI is rising too....

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Quoting WxGeekVA:

It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.




will you this STOP WITH THAT its getinng annoying
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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.