Hurricane Hunters find tropical storm winds in TD 9

By: Dr. Jeff Masters , 7:51 PM GMT on August 21, 2012

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The Air Force Hurricane Hunters are in Tropical Depression Nine, and have discovered a region of 40 - 45 mph winds at the surface, using their SFMR instrument. Flight level winds at their 1000 foot altitude spiked as high as 49 mph. The surface pressure was 1005 mb, a typical one for a weak tropical storm. Based on these measurements, it is highly likely that NHC will name this Tropical Storm Isaac at 5 pm EDT. A large area of dry air lies just to the north of the storm, as seen on water vapor satellite loops, and this dry air is interfering with development, allowing only a few clumps of heavy thunderstorms to fire up near TD 9's center, as seen on visible satellite loops. These loops also show some arc-shaped low clouds expanding away from the heavy thunderstorm area on the south side of the center, showing that TD 9 is ingesting dry air that is creating strong thunderstorm downdrafts, robbing the storm of moisture and energy. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper level outflow channel has opened to the southwest, and another channel is attempting to open up to the north. A large clump of heavy thunderstorms several hundred miles to the southeast of TD 9 continues to compete for moisture, and is interfering with the low level inflow and upper level outflow of the storm. The center of TD 9 will pass about 50 miles to the north of buoy 41101 near midnight tonight. The next hurricane hunter mission into TD 9 is scheduled for 2 am Wednesday, and there will be a new mission launched every six hours. The NOAA jet is first scheduled to fly into the storm on Thursday afternoon, to do a large-scale dropsonde mission to aid model forecasts.


Figure 1. Satellite image of TD 9 and 96L taken at 10:45 am EDT August 21, 2012. The two storms are connected by a thin line of low clouds. Image credit: NOAA Environmental Visualization Lab.

Intensity forecast for TD 9
The latest 2 pm EDT run of the SHIPS model predicts that wind shear will be low to moderate, 5 - 15 knots, for the next five days. Ocean temperatures will warm from 28°C today to 29°C by Wednesday afternoon, and the total heat content of the ocean will increase sharply during that period. The low wind shear and warm waters will favor strengthening. The main impediment to development through Wednesday will be dry air to the north, though the storm will also have trouble separating from the clump of thunderstorms to its southeast. I expect that TD 9 will continue to struggle with dry air through Wednesday. The official NHC forecast is of a 60 mph tropical storm moving through the Lesser Antilles on Wednesday evening; I put the most likely range of strengths for TD 9 Wednesday evening at 50 - 60 mph. Once TD 9 enters the Eastern Caribbean, wind shear will be low, oceanic heat content high, and the storm should have had enough time to moisten the atmosphere to allow steady strengthening to a hurricane. Intensity forecasts 4 - 5 days out are low in skill, though, and it would not be a surprise at all to see TD 9 struggle like so many other storms have over the past two years, and remain a tropical storm over the next five days. Conversely, rapid intensification into a Category 2 hurricane five days from now, as the official NHC is suggesting may happen, would also not be a surprise.


Figure 2. Daily Oceanic Heat Content or Tropical Cyclone Heat Potential (TCHP) for TD 9. The forecast points are from the 11 am EDT NHC advisory, and the 24 hour forecast point shown here is for 8 pm EDT Wednesday. For tropical cyclones in favorable environmental conditions for intensification (i.e., vertical wind shear less than 15 kt, mid-level relative humidity >50 %, and warm SSTs [i.e., >28.5C]) and with intensities less than 80kt, values of ocean heat content greater than 50 kJ/cm^2 (yellow and warmer colors) have been shown to promote greater rates of intensity change. TD 9 will be crossing into such a region early Wednesday morning, and will enter a region of very high TCHP south of Hispaniola on Friday morning (the 72 hour forecast point.) Image credit: NOAA/RAMMB.

Latest model runs for TD 9
The latest set of 12Z (8 am EDT) model runs for TD 9 are fairly unified for the coming three days, showing a west to west-northwest track to a point just south of Hispaniola. Most of the models then predict a more west-northwest track across Southwest Haiti and into eastern Cuba, as TD 9 responds to a small trough of low pressure over the Southeast U.S. A notable exception is our best-performing model, the ECMWF, which keeps TD 9 south of Hispaniola, and takes the storm more to the west over Jamaica by Saturday, and then into the Yucatan Channel between Mexico and Cuba by next Tuesday. We'll have to wait another day to see where the center of TD 9 consolidates before judging which model solution is likely to be correct; reformations of the center closer to bursts of heavy thunderstorm often cause the center point to shift around in the early stages of development, leading to large changes in the forecast track many days later. TD 9 is a threat to affect Tampa during the Republican National Convention, August 27 - 30. I blogged about the climatological chances of a hurricane causing an evacuation of Tampa during the convention in a post last week, putting the odds at 0.2%. The odds in the current situation are higher, probably near 2%. It would take a "perfect storm" sort of conditions to all fall in place to bring TD 9 to the doorstep of Tampa as a hurricane during the convention, but that is one of the possibilities the models have been suggesting could happen.

Disturbance 96L off the coast of Africa
A large tropical wave in the eastern Atlantic about 550 miles southwest of the Cape Verde Islands (Invest 96L) is headed west at 15 mph. This disturbance has an impressive amount of spin, as seen on visible satellite loops, and a respectable amount of heavy thunderstorm activity that is increasing. The storm is under a light 5 - 10 knots of wind shear. Given that TD 9 has moistened up the atmosphere ahead of 96L, this disturbance should have less of a problem with dry air. In their 2 pm EDT Tropical Weather Outlook, NHC gave 96L a 60% chance of developing into a tropical cyclone by Thursday afternoon. This disturbance will track nearly due west the next three days, then is expected to turn more to the west-northwest late this week, bringing it close to the northern Lesser Antilles Islands by Sunday.

Disturbance 95L in the Gulf of Mexico near the Texas/Mexico border
A region of disturbed weather (Invest 95L) is in the Gulf of Mexico, just northeast of Tampico, Mexico. In their 2 pm EDT Tropical Weather Outlook, NHC downgraded the chances of 95L developing to 20%. The Air Force hurricane hunter aircraft scheduled to investigate 95L this afternoon was cancelled. Radar out of Altamira, Mexico does not show any organization to the precipitation echoes and visible satellite loops show that 95L is small and disorganized. The computer models show that 95L should drift westwards, and may move over Mexico on Wednesday.

I'll have a new post in the morning.

Jeff Masters

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4034. AnthonyJKenn
4:49 PM GMT on August 22, 2012



12z GFS @ 156 (8/29): Moving NNE, going inland near FL Big Bend area.

GA/SC gets drought relief, but FL gets soaked, and tornadoes, and  TS/Cat 1 hurricane winds. Tampa's licking their wounds by now.


Member Since: September 20, 2005 Posts: 0 Comments: 209
4033. VINNY04
4:24 PM GMT on August 22, 2012
Quoting Patrap:
Its only Afternoon in Fla.

: P
you in florida too?
Member Since: March 6, 2011 Posts: 0 Comments: 243
4032. Patrap
3:58 PM GMT on August 22, 2012
Its only Afternoon in Fla.

: P
Member Since: July 3, 2005 Posts: 426 Comments: 129093
4031. CatfishJones
3:29 PM GMT on August 22, 2012
Quoting Bluestorm5:
I knew that :) I love going to Wrightsville Beach!

That year sucked; both Fran and Bertha. My family lived in a condo right on the beach (Lumina Club, by The Oceanic/south end pier, if you know the place).
Member Since: May 30, 2008 Posts: 0 Comments: 246
4030. atmosweather
3:28 PM GMT on August 22, 2012
Quoting WxGeekVA:


here fishy fishy fishy...;P



Just for comparison:



Track forecasts out to 5 days or more for weak cyclones are subject to huge changes.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
4029. ncwxman68
3:25 PM GMT on August 22, 2012
Quoting GetReal:
If the low level center is that far north, Isaac is not stacked, and that is a stronger mid level circulation the Barbados radar is picking up.


No...at first I though that too, but it is an illusion caused by its very fast translational speed to the west.
Member Since: August 13, 2009 Posts: 0 Comments: 17
4028. GetReal
3:15 PM GMT on August 22, 2012
If the low level center is that far north, Isaac is not stacked, and that is a stronger mid level circulation the Barbados radar is picking up.
Member Since: July 4, 2005 Posts: 204 Comments: 8898
4027. Patrap
3:12 PM GMT on August 22, 2012
Be safe up dere MLC.

We know how these Big CV ones CAN go,..and I'm sure yer keeping one Eyeball on Him.
Member Since: July 3, 2005 Posts: 426 Comments: 129093
4026. GetReal
3:11 PM GMT on August 22, 2012
An observation with a question... After observing the Barbados radar loops it is clearly visible to anyone that the convection north of Barbados is moving EAST to
WEST. Now if the center of Isaac is currently located at 15.9N as NHC indicated on last advisory, shouldn't the convection on the Barbados radar be moving WEST to EAST. After all doesn't a cyclone rotate counter-clockwise in the N hemisphere?


Link hit the 400km loop.

Member Since: July 4, 2005 Posts: 204 Comments: 8898
4025. Stoopid1
3:10 PM GMT on August 22, 2012
Things are starting to heat up in the tropics now. Very hard to say the exact track of Isaac now after 3 days time. I don't like historical comparisons much, dynamics are always different in some ways, but 1979's Hurricane David has a very similar track to that projected for Isaac. Models seem pretty on and in good agreement from what I'm seeing, but again, can't say for sure. It'll come down to his strength and the break strength on where Isaac will turn north. For now I'd take a middle of the road projection for him, taking him roughly to the Florida Bay.

Oh and I will say though, Isaac looks pretty good from satellite images for a 1006mb storm.
Member Since: August 6, 2007 Posts: 24 Comments: 2752
4024. gulfbeachgal
3:10 PM GMT on August 22, 2012
Quoting SrChiefFan1:


If he shows up there you will be safe. He never shows up at ground zero of a storm....


Agreed!
Member Since: August 28, 2008 Posts: 0 Comments: 25
4023. CJ5
3:10 PM GMT on August 22, 2012
Quoting belizeit:
I think Isaac has degraded into a open wave but its best to keep the warninings up so as to protect life


:facepalm: Posting should require some sort reasonable information.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
4022. Patrap
3:09 PM GMT on August 22, 2012
Quoting moonlightcowboy:



Yup. I'm up mid-state today, beautiful sky and temps. As long as Isaac is sprinting along like it is things could change. Next 24-36 hours will be critical I think. Anything gets in that boiler pot south of us will likely spell trouble somewhere. I keep watching that sfc map, those highs.

Y'all hold the fort down! ;)


This is sum fine weather fer sho MLC.

Be safe and I know you'll on top of things.


Member Since: July 3, 2005 Posts: 426 Comments: 129093
4021. yoboi
3:09 PM GMT on August 22, 2012
Quoting JasonRE:
Chasey: Also here in Louisiana....Lafayette though. Was wondering the same thing. Saw a post earlier saying that it may reduce to a Tropical storm strength after crossing Hispaniola, and track slightly further away

I have work sending me to Houston but I want to be home in case of the rain. Last weekend we got 3 hours of steady, heavy rain and the rain stopped literally right before it flowed over the threshold of our front and back doors. I need to be home just in case. I don't want the wifey home alone during this.


it's always a good idea to have some sand bags prefilled and stored at your house living in la never know when ya might need them...
Member Since: August 25, 2010 Posts: 7 Comments: 2402
4020. Grothar
3:08 PM GMT on August 22, 2012
Quoting drg0dOwnCountry:

Thanks, and do you think that Isaac is changing the high pressure above him already? Maybe what could happen is that the storm moves more westerly from this.


I really don't know. It think it is too early to tell that. Some models still having it moving further west, but they could become the outlier models.
Member Since: July 17, 2009 Posts: 71 Comments: 26865
4019. guygee
3:08 PM GMT on August 22, 2012
Quoting rmbjoe1954:
The NHC should shift the cone to the left adjusting for the 06Z GFS solution.
On the other hand, it is hard to figure the GFS left shift since the trough is there and the W. Atlantic high is far withdrawn. NHC still has plenty of time to analyze, and interaction with land will play a big role in future track.
Member Since: September 16, 2005 Posts: 0 Comments: 3174
4018. SouthTXWX
3:08 PM GMT on August 22, 2012
NEW BLOG
Member Since: February 28, 2012 Posts: 0 Comments: 66
4016. CybrTeddy
3:08 PM GMT on August 22, 2012
I honestly hate these kinds of storms. They look beautiful on satellite, borderline hurricane almost. Yet the recon goes in there and discovers that it's a disorganized tropical storm with 45mph winds tops. There has to be a bigger issue than trade winds that is doing this to so many storms. Dolly, Fay, Ophelia, Maria, Ernesto, and now Isaac have all gone through this zone in the Caribbean and suffered a similar result - having issues with its circulation.
Member Since: July 8, 2005 Posts: 259 Comments: 24477
4015. LargoFl
3:07 PM GMT on August 22, 2012
Quoting hydrus:
We would have a lot better outcome from Isaac if the NOGAPS were to happen.
yes sure would alright
Member Since: August 6, 2011 Posts: 4 Comments: 40968
4014. moonlightcowboy
3:07 PM GMT on August 22, 2012
Quoting Patrap:


Roger dat,

U got yer ear's on MLC?

Big Duke NOLA 7 here.

: )



Yup. I'm up mid-state today, beautiful sky and temps. As long as Isaac is sprinting along like it is things could change. Next 24-36 hours will be critical I think. Anything gets in that boiler pot south of us will likely spell trouble somewhere. I keep watching that sfc map, those highs.

Y'all hold the fort down! ;)
Member Since: July 9, 2006 Posts: 184 Comments: 29610
4013. Maineweatherguy20023
3:07 PM GMT on August 22, 2012
Quoting belizeit:
I think Isaac has degraded into a open wave but its best to keep the warninings up so as to protect life

Those are just the rain bands.. not the CLOSED COC
Member Since: August 1, 2012 Posts: 0 Comments: 269
4012. KEEPEROFTHEGATE (Mod)
3:07 PM GMT on August 22, 2012
Member Since: July 15, 2006 Posts: 175 Comments: 54858
4011. LargoFl
3:07 PM GMT on August 22, 2012
Member Since: August 6, 2011 Posts: 4 Comments: 40968
4010. hydrus
3:07 PM GMT on August 22, 2012
Quoting LargoFl:
We would have a lot better outcome from Isaac if the NOGAPS were to happen.
Member Since: September 27, 2007 Posts: 1 Comments: 21757
4009. WunderAlertBot (Admin)
3:06 PM GMT on August 22, 2012
JeffMasters has created a new entry.
4008. Bluestorm5
3:06 PM GMT on August 22, 2012
Twitter is a great place for professional information from NHC and their units.

@NHC_Surge

NHC forecasting 1-3 ft of storm #surge from #Isaac in the northern Leeward Islands and Puerto Rico
Member Since: August 1, 2011 Posts: 28 Comments: 8041
4007. yoboi
3:06 PM GMT on August 22, 2012
it's intersting that the eqecat model is tracking Isaac...maybe we will see this model added in the future atlantic tracking???
Member Since: August 25, 2010 Posts: 7 Comments: 2402
4005. midgulfmom
3:06 PM GMT on August 22, 2012
Quoting RitaEvac:
Frontal boundary/Trough washing out over Florida

Thanks! Assume little or no affect. Like the pic BTW :)
Member Since: July 9, 2005 Posts: 2 Comments: 1164
4004. LargoFl
3:05 PM GMT on August 22, 2012
Member Since: August 6, 2011 Posts: 4 Comments: 40968
4003. floridaboy14
3:05 PM GMT on August 22, 2012
Quoting CybrTeddy:
NHC says that the CoC of Isaac reformed to the north. That probably explains the sudden disorganization in my opinion. Gradual intensification, not rapid, should be expected. I think it will peak out at 50mph today, and hit Haiti as a 70-75mph system. Anything beyond that is a mystery to me. I will be honest as I try not to be egotistic on here - I have no idea where this thing is going after Haiti. There's evidence to support Levi's prediction that it begins to recurve towards the US East Coast, and there is ample evidence to support that it could probably end up hitting Florida. Either way, I suspect that even if it doesn't strengthen before the system hits Haiti, that intensification is likely after it passes the island.
15.9N isnt that big of a shift compared to 15. 7 :) its moving due west now and is getting impacted by northeasterly shear and dry air which should keep it weaker and on a more southerly track in my opinion
Member Since: July 25, 2011 Posts: 0 Comments: 1102
4002. JasonRE
3:05 PM GMT on August 22, 2012
Chasey: Also here in Louisiana....Lafayette though. Was wondering the same thing. Saw a post earlier saying that it may reduce to a Tropical storm strength after crossing Hispaniola, and track slightly further away

I have work sending me to Houston but I want to be home in case of the rain. Last weekend we got 3 hours of steady, heavy rain and the rain stopped literally right before it flowed over the threshold of our front and back doors. I need to be home just in case. I don't want the wifey home alone during this.
Member Since: August 6, 2012 Posts: 0 Comments: 122
4001. SouthTXWX
3:05 PM GMT on August 22, 2012

Quoting StormTracker2K:


That is one big ASS storm. Geesh!
Flagged and reported, please keep comments G rated.
Member Since: February 28, 2012 Posts: 0 Comments: 66
4000. Maineweatherguy20023
3:05 PM GMT on August 22, 2012
TD 10 YAY!! Why does the nhc track soooo far north??
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3999. TropicalAnalystwx13
3:05 PM GMT on August 22, 2012
Quoting WxGeekVA:


here fishy fishy fishy...;P


That doesn't look fishy fishy...
Member Since: July 6, 2010 Posts: 113 Comments: 32527
3998. unknowncomic
3:04 PM GMT on August 22, 2012
We need to think about those first in Isaac's path--Hispanola and other. Especially Haiti.
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3997. hydrus
3:04 PM GMT on August 22, 2012
This could hammer the west coast of Florida with prolonged hurricane force winds and heavy rain.
Member Since: September 27, 2007 Posts: 1 Comments: 21757
3996. Bluestorm5
3:04 PM GMT on August 22, 2012
@NHCDirector

Next Air Force C130J mission into #Isaac departing noon EDT/AST today, investigating storm thru about 8 pm tonight.
Member Since: August 1, 2011 Posts: 28 Comments: 8041
3995. SFLWeatherman
3:03 PM GMT on August 22, 2012
Hey i'm in WPB and the track will shift back 5day out we all do not if it a E FL or W FL landfall!!
Quoting 7544:
not a good location for landfall that means se fla will be on the est side of the storm which means worst conditions i liked the old track better ut it still could shift back
Member Since: May 23, 2012 Posts: 0 Comments: 4949
3994. LargoFl
3:03 PM GMT on August 22, 2012
Member Since: August 6, 2011 Posts: 4 Comments: 40968
3993. Bluestorm5
3:03 PM GMT on August 22, 2012
Quoting Brock31:


That was filmed right here at Wrightsville Beach.

I got Cantore's autograph when he was here in 96 for Fran.....yes, I want a cookie
I knew that :) I love going to Wrightsville Beach!
Member Since: August 1, 2011 Posts: 28 Comments: 8041
3992. johnbluedog69
3:03 PM GMT on August 22, 2012
Good morning pat,press,and grothar.Hope you folks are well today.
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3991. Patrap
3:02 PM GMT on August 22, 2012
A Bigger Ballerina takes a lot mo time to bring her arms in and consolidate some decent Mojo one could say.




Member Since: July 3, 2005 Posts: 426 Comments: 129093
3990. Grothar
3:02 PM GMT on August 22, 2012
Quoting WxGeekVA:


here fishy fishy fishy...;P



I don't buy. The models are way off. It can't go that way. It will turn WSW. They don't know what they're doing. It will be much stronger, it will be much weaker. :):):)
Member Since: July 17, 2009 Posts: 71 Comments: 26865
3989. RitaEvac
3:01 PM GMT on August 22, 2012
Frontal boundary/Trough washing out over Florida
Member Since: July 14, 2008 Posts: 1 Comments: 9648
3988. CybrTeddy
3:01 PM GMT on August 22, 2012
NHC says that the CoC of Isaac reformed to the north. That probably explains the sudden disorganization in my opinion. Gradual intensification, not rapid, should be expected. I think it will peak out at 50mph today, and hit Haiti as a 70-75mph system.

Anything beyond that is a mystery to me. I will be honest as I try not to be egotistic on here - I have no idea where this thing is going after Haiti. There's evidence to support Levi's prediction that it begins to recurve towards the US East Coast, and there is ample evidence to support that it could probably end up hitting Florida. Either way, I suspect that even if it doesn't strengthen before the system hits Haiti, that intensification is likely after it passes the island.
Member Since: July 8, 2005 Posts: 259 Comments: 24477
3987. LargoFl
3:01 PM GMT on August 22, 2012
Member Since: August 6, 2011 Posts: 4 Comments: 40968
3986. midgulfmom
3:00 PM GMT on August 22, 2012
What affect will that plunging loop of air down from FLA. and around the islands have on Issac if any? Check WV loop....TIA
Member Since: July 9, 2005 Posts: 2 Comments: 1164
3985. EcoLogic
3:00 PM GMT on August 22, 2012
Size-wize, Issac may end up looking like his "I" brethren.



Member Since: June 29, 2010 Posts: 0 Comments: 53
3984. SFLWeatherman
3:00 PM GMT on August 22, 2012
12Z they have it going up to cat 2 and 3

Member Since: May 23, 2012 Posts: 0 Comments: 4949

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.