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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1474. HrDelta
Quoting Chiggy:
Latest Recon Flight, courtesy of Levi:


Definitely strengthened. At least to 50 mph. Maybe even 60.
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Quoting Tazmanian:
recon found 998mb


998.9 mb
(~ 29.50 inHg)
Interested to see the upcoming VDM.
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1472. wpb
recon headed home
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Quoting Tazmanian:
recon found 998mb


998.9 mb
(~ 29.50 inHg)


Recon is ascending, so they are headed home.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Recon instrument failure.
They passed through the center... but No pressure measurements were taken.
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Quoting Dunkman:


Then again the Euro rather substantially outperformed NHC forecasts after 72h so... I agree that I think the Euro scenario is somewhat unlikely and would need to see it probably on the next 2 runs before I really bought in, but you just can't discard the model that not only beats the other models but also the team of our best forecasters.


I Love it...Point.......Counterpoint. All included in my $14.95 DSL bill.
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Extrapolated
Surface Pressure

15.817N 66.833W

998.9 mb
(~ 29.50 inHg)


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Quoting Tazmanian:
recon found 998mb


998.9 mb
(~ 29.50 inHg)


They were ascending when the found that
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Issac's core is so disorganized, it's almost pissing me off as much as Ernesto lol.
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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
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1464. angiest
Quoting aislinnpaps:


And Lili.


Ah yes, Lili. Strong cat 4 until maybe a day before landfall, then the core collapsed. Close call on that one.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Post# 1295
Quoting MAweatherboy1:
Tembin has made landfall on Taiwan:


The whole country is under that system. I hope they are ok.
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1461. emguy
Quoting Chiggy:

HUH? What's going on there? Most of Issac's mass in now either South or SSW of the island of PR..


Check out the radar and see...There is other rotation...suggesting the system is either highly elongated, or we have a binary low. This storm is a hot mess right now.
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recon found 998mb


998.9 mb
(~ 29.50 inHg)
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This storm has not intensified like the NHC thought it would...the forecast at 4pm yesterday had it at a 60mph TS a 2 pm today and a hurricane by friday afternoon
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1457. Chiggy
Quoting Gearsts:
Center moving north towards PR or the Mona Passage? Guys look at the lower clouds movement.Link

Please stop putting garbage on here.. thx
Member Since: June 26, 2012 Posts: 0 Comments: 297
1456. atl134
Quoting TexNowNM:
IF Isaac were to Hit the Tx/La border what kind of time frame would be involved. Some of you are pretty good at calculating these sorts of things. Yes, I know that is an outlier destination- just asking for a reasonable time frame.


The ECMWF has it at Louisiana around 144hr so... sometime the 29th give or take a day IF it were to go to TX/LA.
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Quoting HurricaneDean07:

That vortex message was before they went into other parts of the storm..
They've found 45 Mph winds... and 50 Mph Flight level winds.


Roger that. Image was from 2pm EDT
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Quoting weatherguy03:


Thanks. I used to have a blog on this site for many years but I have moved. I try not to talk too much on the main blog here because it can get alittle crazy to say the least at times. I dont know how Levi does it!..LOL If you want you can follow me on Youtube and subscribe to me just in case I dont put it in this blog. I dont always. Just look for weatherguy03 on You Tube.



Or you can be his friends on Facebook and he will give you the info!

Hi Bob!!!! Glad to see you stop by here today.
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Quoting Kowaliga:
Nice pull to the N....he roundin' the bend?



You might be accused of heresy!
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?? Traveling into center reported the following??

SFMR
Peak (10s Avg.) Sfc. Wind

67 knots
(~ 77.0 mph)

73 knots*
(~ 83.9 mph*)
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Recon found CONTAMINATED reports of 80mph and 85mph. :P
Member Since: July 14, 2009 Posts: 51 Comments: 1731
Recon confirms the center is closer to 15.6N moving just barely north of west.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Models surely west today, back east tomorrow? Stay Tuned.

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Quoting 1900hurricane:

Nope, no one has mentioned it since I have been on today. It sure was bizarre to watch when it happened.

Maybe it'll make the post-season discussion. There were HHs up in it while it happened.... easily the most bizarre thing I've seen in developing cyclones.
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Quoting scott39:
Does the central and W side of Cuba have mountains?

Yes, but most of the mountains are in the east. Check this out
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1445. Chiggy
Quoting emguy:
I think Levi might be right about something going on further north...closer to Puerto Rico. The radar imagery out of San Juan is showing some hints of this. At first, I had to do a double take...but something is going on...and it's not where we thought the center was at.

Link


HUH? What's going on there? Most of Issac's mass in now either South or SSW of the island of PR..
Member Since: June 26, 2012 Posts: 0 Comments: 297
Quoting mikatnight:



That vortex message was before they went into other parts of the storm..
They've found 45 Mph winds... and 50 Mph Flight level winds.
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Quoting CarolinaSoxfan:


Yep, I have been saying all along that Sfla would dodge another bullet but everyone gets upset and calls me a troll!!!! Well to that I say suck it!!!!



This is 953soxfan, he is a troll notice the join date
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IF Isaac were to Hit the Tx/La border what kind of time frame would be involved. Some of you are pretty good at calculating these sorts of things. Yes, I know that is an outlier destination- just asking for a reasonable time frame.
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1440. Gearsts
Center moving north towards PR or the Mona Passage? Guys look at the lower clouds movement.Link
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Quoting ILikeIke:
isaac reminds me of Ike. They both were pretty large and I think if I remember right they though Ike was going to hit florida too. hmmmmmm

Ike was forecasted to head up the East coast. But Ike pumped the ridge and slammed into Cuba... And... We know what happened after...
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Quoting MarkTodd2233:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 23rd day of the month at 18:34Z
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: 7
Observation Number: 09
A. Time of Center Fix: 23rd day of the month at 17:51:40Z
B. Center Fix Coordinates: 15°39'N 66°26'W (15.65N 66.4333W)
B. Center Fix Location: 193 miles (310 km) to the S (187°) from San Juan, Puerto Rico (USA).
C. Minimum Height at Standard Level: 1,459m (4,787ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 22kts (~ 25.3mph)
E


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Quoting aislinnpaps:


And Lili.


Them too.
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Quoting Bluestorm5:
Can we please discuss what's going on with Isaac right now? I want to know more about it. Like... is the storm stronger or weaker than a few hours ago.


Hurricane hunter Info suggest this will likely be a 45mph storm moving WNW turn.
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From the NOAA G-IV flight, ridging is holding on strong off the coast of FL. Still a nice ridge of nearly 590DM. Winds out of the SE at the 500mb level.

500mb 5,890m (19,324 ft) -8.1%uFFFDC (17.4%uFFFDF) Approximately -25%uFFFDC (-13%uFFFDF) 140%uFFFD (from the SE) 14 knots (16 mph)
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1434. Chiggy
Quoting MarkTodd2233:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 23rd day of the month at 18:34Z
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: 7
Observation Number: 09
A. Time of Center Fix: 23rd day of the month at 17:51:40Z
B. Center Fix Coordinates: 15°39'N 66°26'W (15.65N 66.4333W)
B. Center Fix Location: 193 miles (310 km) to the S (187°) from San Juan, Puerto Rico (USA).
C. Minimum Height at Standard Level: 1,459m (4,787ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 22kts (~ 25.3mph)
E


I can live with 15.4degs as my guess was around 15N and 66.5W
Member Since: June 26, 2012 Posts: 0 Comments: 297
Link

Look at 14.8N/66.8W and tell me what you see.
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1432. emguy
I think Levi might be right about something going on further north...closer to Puerto Rico. The radar imagery out of San Juan is showing some hints of this. At first, I had to do a double take...but something is going on...and it's not where we thought the center was at.

Link

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1431. angiest
Quoting 1900hurricane:

At this point, it seems highly unlikely. However, at more than five days out, it can't be completely discounted. In three days time, things will be a little more certain.


In the (admittedly unlikely) event Isaac were to come this far west, we are probably at about 7 days. This is Ike's cone at roughly 7 days from final landfall.



Shows how much can change in a week. At around the time of this forecast, a lot of people on this blog said it wouldn't happen.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1430. DVG
Quoting cirrocumulus:



It does appear to be consolidating a little south of NOAA forecast tracks.


It seems that to as well, but not but much. The motion seems to parallel the forecast track also.

These sat pix can trick one easily. I'm also wondering if the tstorm to the right of the clear area might not be the center.

In any case, the circulation looks better to me than any time I've seen.
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Quoting KeyWestbeachcomber:
Key west here...ya'll think I should get some groceries in? Any input appreciated,thanks.


Good idea. If you pick up some nice salmon steaks and a decent Moscato, I'll stop by for dinner.
Member Since: March 9, 2012 Posts: 0 Comments: 150
This is another garbage storm traversing the Caribbean. I'm making my final take on this storm and standing down I quit.A few days ago Doc Masters said it might not develop and head into Mexico like Ernesto,I'm going with that.The price of gasoline going up .13 cents in the last few days and everybody running to the pumps and stores is a joke 5 to 7 days a head. Just a bunch of sheep getting sheared by the mass media. These five day forecast being overblown by the media, is going to backfire some day. My useless rant but I feel better. My only regret is not that I said this standby RI Flag on sorry in advance.
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Quoting sullivanweather:


It isn't so much that the center keeps reforming...

It's more that there hasn't been a true inner core of the system, but rather a board tropical low pressure system. These center reformations are simply individual vorticies spinning around the overall broad circulation, which would be much easier to discern in a system with less convection. These little vorticies would eventually take over and become the dominant center is a smaller, more symmetric storm. But due to the large, broad, off-centered nature of Isaac these little areas of vorticity get spun off. As they spin off they sometimes drag the broader center in their direction but never far enough to change a longer term vector, which is why the storm 'center' (area of lowest pressure) has remained north of 15°N, despite all these apparent 'jumps' of the center. It's simply a representation of how the storm is currently structured.
Nicely put. Dry air and fast forward motion have prevented the storm from building that solid inner core and getting a well defined closed circulation despite a large anticyclone present aloft providing light shear and divergence over warm waters. Forward motion has since slowed since yesterday but dry air is still a problem.

Quoting sullivanweather:


Me?? lol

I've been here forever...

And thank you.
I can tell, but I wish you posted more on our tropical developments lol
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Quoting redwagon:

Was there any discussion today of that monster convective column we were watching 11p last night jump up and pounce on the SW side? 'Alien scud blob' I think was its name at the time.

Nope, no one has mentioned it since I have been on today. It sure was bizarre to watch when it happened.
Member Since: August 2, 2006 Posts: 47 Comments: 11709
Quoting Jedkins01:



Hey, this is a bit off topic, but I thought I'd just let you know, you do a great job here and you have a brilliant mind for meteorology, don't let envious and contentious people bother you...


agreed! 100%
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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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