Little change to Isaac, but intensification coming; Joyce forms

By: Dr. Jeff Masters , 3:13 PM GMT on August 23, 2012

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Tropical Storm Isaac is a large and impressive-looking storm on satellite images, but data from the Hurricane Hunters reveal that Isaac remains a minimal-strength tropical storm with 40 mph winds, as it heads westward across the Eastern Caribbean. An Air Force Reserve hurricane hunter aircraft which completed its mission into Isaac at 8 am EDT found top winds at the surface near 40 mph, and highest winds at their 5,000 foot flight level of 47 mph. A NOAA hurricane hunter aircraft flying at 10,000 feet has found top winds of 47 mph at that altitude. The Hurricane Hunters found a broad area of light winds with a central pressure of 1003 mb. The aircraft did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. There does not appear to be much in the way of dry air near the core of Isaac, as seen on water vapor satellite loops, which is a big switch from what we've seen previously. Visible satellite loops show that Isaac has a much more symmetric circular cloud pattern, and has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of an intensifying storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper-level pattern of outflow supportive of significant strengthening has developed this morning, with an upper-level outflow channel now well-established to the north, and a new outflow channel opening to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and becoming more organized.


Figure 1. Morning radar image of Isaac taken from the Puerto Rico radar. Isaac's rain bands are weak, but are starting to take on a more spiraling shape.

Intensity forecast for Isaac
Isaac has consistently confounded predictions that it would intensify, but all the potential factors inhibiting intensification seem to have diminished to the point where intensification has to occur. Wind shear is low, 5 - 10 knots, and ocean temperatures are warm, 29°C, and these warm waters extend to great depth, giving the storm a high total heat content to work with. These factors, combined with the favorable upper-level outflow pattern and more symmetric cloud pattern, support intensification, and all of the intensity models except the HWRF model predict intensification of Isaac to a strong tropical storm or Category 1 hurricane by Friday afternoon. The latest 8 am EDT run of the SHIPS model predicts that wind shear will be light to moderate, 5 - 15 knots, for the next five days. The 11 am EDT wind probability forecast from NHC predicted a 34% chance that Isaac will become a hurricane by Friday afternoon, and a 6% chance it will be a Category 2 or stronger hurricane then. By Friday afternoon, Isaac will likely be close enough to Southwest Haiti that the inner core will be disrupted, and the storm will likely be a 45 - 55 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, and the upper-level wind pattern favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane.

Impact of Isaac on the Islands
The south coast of Puerto Rico should see Isaac's heaviest rains and strongest winds beginning near 8 pm EDT tonight, with tropical storm-force winds of 40 - 45 mph potentially affecting the southwest portion of the island. The San Juan airport may be able to stay open during Isaac's passage, but with delays when spiral bands move overhead.

Heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic late tonight, and the Santo Domingo airport will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.

Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.

Impact on Florida, Cuba, Jamaica, and the Bahamas
Florida, Cuba, Jamaica, and the Bahamas are all at risk of receiving flooding rains and high winds from Isaac. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a west-northwestward track over Southwest Haiti and into Western Cuba. At the 4 - 5 day forecast period for Sunday and Monday, the models have come into better agreement, and have shifted west some. Our best-performing model, the ECMWF, has now shifted Isaac's path more to the east, but still is the westernmost of the models, predicting a landfall for Isaac near the Alabama/Florida border on Wednesday. While we do still have some models predicting a path up the east coast of Florida, model consensus now favors a path up the west coast of Florida through the Gulf of Mexico. The recent reformation of Isaac's center more to the south supports the idea that Isaac will take a track more to the west through the Gulf of Mexico. Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall. The NOAA jet is scheduled to fly into the storm this afternoon, to do a large-scale dropsonde mission to aid model forecasts. These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

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 15% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. The latest model tracks for Isaac suggests that the trough of low pressure pulling the storm to the north will not be strong enough to give Isaac a northeastward component of motion when it crosses Tampa's latitude. Thus, Isaac will have difficulty making a direct hit on Tampa without passing over a considerable amount of land first, making a multi-billion dollar hurricane disaster in Tampa very unlikely. I put the odds of a mass evacuation occurring during the convention at 1%; a limited evacuation of people in the Tampa Bay area living in mobile homes in low-lying areas is probably about 5 - 10 % likely. I have detailed information on Tampa's storm surge vulnerability in a post from last week.


Figure 2. Morning satellite image of Tropical Storm Joyce.

Tropical Storm Joyce forms in the Central Atlantic
The season's tenth named storm of the year, Tropical Storm Joyce, has formed in the Central Atlantic. Joyce's formation on August 23 puts 2012 in a tie for second place with 1995 for earliest formation date of the season's tenth storm. Only 2005 had an earlier appearance of the season's tenth storm, when Tropical Storm Jose formed at 2 pm EDT on August 22. None of the models show that Joyce will be a threat to the Lesser Antilles Islands, but it may be a storm that will affect Bermuda. It is possible that Joyce will complicate the track forecast for Isaac 4 - 5 days from now, when the storms may be close enough together to interact.

Jeff Masters

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1524. CJ5
Quoting KeyWestbeachcomber:
Key west here...ya'll think I should get some groceries in? Any input appreciated,thanks.


Considering all major model put the storm in your front door, yes, I would make some preparations.
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It was post 1492...
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Quoting stormpetrol:


Yep, I see it in that area too, but looks like an eye wall might build up starting just below 15N.

Microwave?
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Quoting GTcooliebai:
Alright who was the wise guy that stretched the blog?
1492....
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1520. Joe21
Does anyone fail to relize that even if the storms rides the west coast of fl or near it that people on the east coast will get the worse of the storm.just indications pount to gulf of mex does not mean the east coast of fl is out of the woids.Just be clear on that.

And another thing it seems like of you want the storm to come to your area so you can prove your right.Lets be real the storm goes wherever mother nature wants it to go not you.Lets not get people off guard.
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1519. Buhdog
Quoting indianrivguy:


just say no


What up river guy... been awhile.

Just to show you how much off of florida the forecast has become...

Link
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1518. snotly
Ike was just as bad.

Quoting MiamiHurricanes09:
Issac's core is so disorganized, it's almost pissing me off as much as Ernesto lol.
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Wouldn't be surprised to see another small westward adjustment with the track at 5 pm. Nothing major until the G-IV data tonight. 
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Quoting MississippiWx:


Recon had ascended when they got that reading. They are leaving.
Oh, can't say I'm surprised; Isaac is still so disorganized a sub-1000mb is rather unrealistic.
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Quoting hurricanejunky:


Isaac definitely not living up to the legacy of "I" storms...Ivan...Ike...Irene...Isabelle...

YET!!!

120 hrs GFS...
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Alright who was the wise guy that stretched the blog?
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Quoting MiamiHurricanes09:
Simply put, if Isaac strengthens, south Florida is screwed, if it remains weak, it should be a southern Keys/Florida Straights event.


I'm thinking that's why the models continue to shift. Despite looking impressive earlier today, dry air looks like it's still causing big problems for it and the weaker it stays the less poleward it moves...
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Quoting StormTracker2K:


I have no problems with the track but Issac seems to be getting much stronger right now. I bet we have a hurricane at 11pm. Also wouldn't rule out a cat.2 100mph storm making landfall in Haiti.

Notice this big blob to the south now starting to wrap around Issac's center.
LOL at your hyping earlier today.  Not sure what weather tools you are using but i'd head to Home Depot and pick up some new ones guy!
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Comment 1492:

You've broken the blog...Please edit or remove your comment.
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Quoting MiamiHurricanes09:
Issac's core is so disorganized, it's almost pissing me off as much as Ernesto lol.


I completely agree. Lol I have been asking why he wont organize. Conditions are so good
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Quoting Bluestorm5:
Freaking recon equipment failures...

yep. was wondering why it would leave the storm already.
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1507. GetReal
Quoting stormpetrol:
Link

Look at 14.8N/66.8W and tell me what you see.



I dunno but it does have clouds wrapped all the way around it moving in a counter-clockwise direction... But I'm sure it isn't anything to concern yourself with...

THERE IS NOTHING TO SEE HERE FOLKS!!! Just keep moving on along... s)
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Quoting louisianaboy444:


I see the center right around 15.3 N


Yep, I see it in that area too, but looks like an eye wall might build up starting just below 15N.
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Quoting MississippiWx:


Recon had ascended when they got that reading. They are leaving.

That was a quick pass... Didnt investigate Isaac, much.
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Splash Location: 15.77N 66.59W
Splash Time: 19:20Z


1004mb (Surface)
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Quoting angiest:


Ah yes, Lili. Strong cat 4 until maybe a day before landfall, then the core collapsed. Close call on that one.


Close call. We lost electric for four days, saving grace was it was early October and cool days, not 100 degrees out. Of course the bad part was it was Fair and Rodeo days, and we were off school to be able to go. I think teachers hate losing free days more than the kids! *G*
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Center is exposed to view @ 15.6N 67.5

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Recon must be having issues if they are leaving so early. Seems a little strange to only have 2 center passes and never sample the SW side of the system where the most convection is located. Regardless, Isaac is status quo and still very disorganized.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting clwstmchasr:


Since '08! Tampa has had a major since 1921.



the reason I made that comment - somebody made the statement that LA/TX has had "several" storms in the past 5 years - just a slight exaggeration......

if you're lucky, Tampa will dodge a bullet with Isaac....
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1497. JLPR2
Hmm.. Well, I think PR dodged one, though our problems could begin with the area of convection west of the Lesser Antilles and get worse depending on where Isaac crosses Hispaniola.



Also, 7,000th post on this account! :)
12,219 posts overall.
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Well to my untrained eye I see the true center at around 15.3 N heading about 275-280 degrees...that is just my take
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Quoting stormpetrol:
Link

Look at 14.8N/66.8W and tell me what you see.

looks like LLC Waiting for recon to pass it to confirm
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Quoting FLHurricaneHunter:
?? Traveling into center reported the following??

SFMR
Peak (10s Avg.) Sfc. Wind

67 knots
(~ 77.0 mph)

73 knots*
(~ 83.9 mph*)

I'll bet that is contaminated data...those are the only two entries showing as such
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Quoting LargoFl:


just say no
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.

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I'm becoming increasingly worried about Isaac. In addition to the fact that this is moving just north of west when it should be moving northwest, this motion also ultimately puts it farther west into the East Gulf of Mexico. This gives it a lot more time to intensify under favorable conditions. It would not surprise me if we have a Category 2 or Category 3 hurricane landfall in Florida/Mississippi/Alabama by the middle of next week.
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HHs headed home!
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Freaking recon equipment failures...
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Quoting angiest:


Ah yes, Lili. Strong cat 4 until maybe a day before landfall, then the core collapsed. Close call on that one.


Yep she was one of my evacuations but she didn't come this far though. Sitting south of Port Arthur as a major leaving seemed like a good idea at the time. :)
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Quoting louisianaboy444:


I see the center right around 15.3 N

No.
Center fix at 15.7... Latest recon.
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1486. TX2FL
Quoting NICycloneChaser:
Yesterday's 12Z EURO: "Yeah, I should probably nudge east a bit.

00Z EURO: "Yeah those other guys are probably on to something. East we go."

Today's 12Z: "Nah, screw that, I'm going to Texas."


As the famous quote says "Ya'll can go to He**, I'm going to Texas!"
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Quoting MiamiHurricanes09:
Interested to see the upcoming VDM.


Recon had ascended when they got that reading. They are leaving.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Recon is lifting out they are already at 14000 ft
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1483. Gearsts
Quoting Chiggy:

Please stop putting garbage on here.. thx
Open your eyes dude.
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The plane is leaving Isaac and going higher. That's why the winds is high and pressure is low.
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Quoting KeyWestbeachcomber:
Key west here...ya'll think I should get some groceries in? Any input appreciated,thanks.


If you want to avoid the rush and long lines tomorrow after the "probable" warnings/watches goes up, you should do your shopping today.
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Quoting stormpetrol:
Time: 19:22:30Z
Coordinates: 15.6167N 66.5W
Acft. Static Air Press: 842.9 mb (~ 24.89 inHg)
Acft. Geopotential Hgt: 1,516 meters (~ 4,974 feet)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 202° at 25 knots (From the SSW at ~ 28.7 mph)
Air Temp: 13.8°C* (~ 56.8°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 28 knots (~ 32.2 mph)
SFMR Peak (10s) Sfc. Wind: 67 knots (~ 77.0 mph)
SFMR Rain Rate: 52 mm/hr (~ 2.05 in/hr)
(*) Denotes suspect data


2"/hr tells you everything you need to know...
I always am skeptical when the surface winds are higher than flight level
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This storm might never develop, and if it continues on this, it's going all the way to Yucatan and show over folks, wait for next storm.

But....models say it's gonna strengthen so lets sit back and watch and watch the NW turn.
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Quoting clwstmchasr:


Since '08! Tampa has had a major since 1921.
You need to clarify that statement, Tampa hasn't had a direct hit by a major since 1921, it has had many close calls since then and recorded hurricane force winds.
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Quoting MississippiWx:
Recon confirms the center is closer to 15.6N moving just barely north of west.
moving west but showing a sign of wnw soon. glad hh confirmed this. thanks for the update mississippi
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting stormpetrol:
Time: 19:22:30Z
Coordinates: 15.6167N 66.5W
Acft. Static Air Press: 842.9 mb (~ 24.89 inHg)
Acft. Geopotential Hgt: 1,516 meters (~ 4,974 feet)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 202° at 25 knots (From the SSW at ~ 28.7 mph)
Air Temp: 13.8°C* (~ 56.8°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 28 knots (~ 32.2 mph)
SFMR Peak (10s) Sfc. Wind: 67 knots (~ 77.0 mph)
SFMR Rain Rate: 52 mm/hr (~ 2.05 in/hr)
(*) Denotes suspect data

Suspect. Rain rate too high. and The fact that the surface wind is Double the flight level winds... Also makes it suspect.
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Quoting stormpetrol:
Link

Look at 14.8N/66.8W and tell me what you see.


I see the center right around 15.3 N
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1474. HrDelta
Quoting Chiggy:
Latest Recon Flight, courtesy of Levi:


Definitely strengthened. At least to 50 mph. Maybe even 60.
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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.

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