Western Caribbean disturbance 99L near tropical depression strength

By: Dr. Jeff Masters , 1:33 PM GMT on October 20, 2010

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A tropical disturbance (Invest 99L) near the Cayman Islands is drifting eastwards towards Jamaica, and has changed little in organization this morning, but is very close to tropical depression status. The storm is bringing heavy rain to the Cayman Islands; 3.85" inches has fallen over the past 48 hours at Savannah on Grand Cayman Island. Heavy rains will continue over the Cayman Islands today and spread to western Jamaica this afternoon. Recent satellite imagery shows that 99L has a well-defined surface circulation, but the center is exposed to view and 99L has a relatively meager amount of heavy thunderstorm activity. Wind shear is marginal for development, 15 - 20 knots, due to the clockwise flow of air around an upper-level high pressure system near the coast of Honduras. The high is bringing strong upper-level winds out of the southwest to 99L. Water vapor satellite loops show considerable dry air to the west and north of 99L, and the strong southwesterly winds over the storm are bringing some of this dry into into the core of the storm, keeping all the heavy thunderstorm development confined to the east side of the center. The waters beneath 99L are very warm, 29°C, but 99L will not be able to take advantage of these warm waters until the shear relaxes. The Hurricane Hunters will be in 99L around 11am EDT this morning to see if the storm is indeed a tropical depression.

Forecast for 99L
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will stay marginal for development, 15 - 25 knots, for the remainder of today, then decline to the moderate range, 10 - 20 knots, on Tuesday, as 99L positions itself more underneath the upper-level high near the coast of Honduras. Any motion by 99L to the southwest will tend to decrease the shear over 99L, and any motion to the north or east will increase the shear, so 99L's current eastwards drift is detrimental for development. Steering currents will be weak Wednesday through Friday in the Western Caribbean, making it difficult to predict where 99L may wander to, and how much shear might affect the storm. By Saturday, a ridge of high pressure is expected to build in to the north of 99L, forcing the storm on a generally westward track. This should allow 99L to find an environment with less shear. The GFDL and HWRF model predicts a more west-northwestward track, with 99L passing through the Yucatan Channel between Cuba and Mexico on Sunday or Monday as a hurricane. The GFS, ECMWF, and NOGAPS models predict a more west-southwesterly path, with 99L making landfall in Belize Sunday or Monday. NHC is giving 99L a 70% chance of developing into a tropical depression by Friday; I'd put these odds at 80%, and expect this will become Tropical Storm Richard by Thursday.


Figure 1. Morning satellite image of Invest 99L.

Death toll from Super Typhoon Megi in the Philippines remarkably low
The power is still out and communications are down over the majority of the northern portion of the Philippines' Luzon Island blasted by Typhoon Megi yesterday, so the full extent of the destruction wrought by the great storm is still unclear. However, the death toll from the great storm stands at only 19, reflecting the superior effort Philippines officials made to evacuate low-lying areas and get people out of locations prone to flash flooding and mudslides. Previous major typhoons to strike the Philippines have nearly always killed hundreds, and sometime thousands, so the preparation and evacuation efforts for Megi likely saved hundreds of lives. Megi hit Luzon on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Severe damage was done to Isabela Province in northern Luzon, and media reports indicate that 200,000 people are homeless.


Figure 2. Visible MODIS satellite image of Megi from NASA's Aqua satellite taken at 1:30am EDT October 20, 2010. At the time, Megi was a Category 4 typhoon with 135 mph winds. Image credit: NASA.

Passage over Luzon Island destroyed Megi's eyewall and inner core region, and the storm compensated by expanding and intensifying the portions of its circulation that were over water. Now that its center is back over water in the South China Sea, Megi has re-developed its inner core and has intensified into a formidable Category 4 typhoon with 135 mph winds. Megi has been able to maintain its larger size, and is now a much larger typhoon than when it hit the Philippines. This is similar to what happened to Hurricane Ike in 2008 when it passed over Cuba, and helped give Ike a very destructive storm surge when it came ashore over Texas. Wind shear is a low 5 - 10 knots over Megi, and the waters of the South China Sea have a very high total heat content to great depth, so Megi should be able to remain a very dangerous major typhoon through Friday. The larger size of Megi means that it will be able to deliver a significant storm surge in excess of ten feet to the coast of China of Friday or Saturday, when the storm is expected to make landfall north of Hong Kong. As the storm approaches the coast on Friday, wind shear is expected to rise to the moderate or high range, and the total heat content of the ocean will drop significantly, so some weakening is to be expected. Still, Megi will probably hit China as a major Category 3 typhoon, bringing a significant storm surge, high winds, and widespread torrential rains that will likely make this a multi-billion dollar disaster for China. The outer rain bands of Megi are already affecting the coast of China north of Hong Kong, as seen on Hong Kong radar and Taiwan radar.


Figure 3. Still frame of damage to NE Luzon Island from a video posted to YouTube by storm chaser James Reynolds of typhoonfury.com.

Next update
I'll have an update later today, with the timing depending upon what the Hurricane Hunters find.

Jeff Masters

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Anyway I am out for now. Will check back later.
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Quoting scott39:
If 99L continues to move ESE, will this help it in reference to wind shear?


No it won't because the anticyclone that is shearing it is moving to the N and will then impart NW shear over 99L. To me it would appear the system is sagging straight to the South now in the visible loop
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this what I say guys 99L is moving SS-SSE I expect a turn to the East and then The N-NNW there after the only reason why 99L is moving south is because it wants to have the ULHigh right over it so it can do what the Gfdl and the Hwrf wants to do with it any way I have to run I'll come back at around 12
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Quoting cat5hurricane:

Yeah it's gone a bit downhill for 99L since this morning.
If the GEM model is right, there will be a wet period for the South Eastern United States....Link
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Quoting kmanislander:


I posted some of that imagery last night when the convection was disappearing. The key to this IMO is that 99L cannot fight off both the dry air and shear. One or other have to let up for it to stand a chance. The dry air is not going away any time soon but if the high centers overhead the system it would allow it to build some convection over the core and potentially hold the dry air at bay.

I guess we will just have to wait and see how this plays out. Not looking too good right now and a lot worse than 8 this morning when it seemed close to being classified.

Yeah it's gone a bit downhill for 99L since this morning.
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Quoting kmanislander:


I posted some of that imagery last night when the convection was disappearing. The key to this IMO is that 99L cannot fight off both the dry air and shear. One or other have to let up for it to stand a chance. The dry air is not going away any time soon but if the high centers overhead the system it would allow it to build some convection over the core and potentially hold the dry air at bay.

I guess we will just have to wait and see how this plays out. Not looking too good right now and a lot worse than 8 this morning when it seemed close to being classified.
If 99L continues to move ESE, will this help it in reference to wind shear?
Member Since: June 13, 2009 Posts: 0 Comments: 6881
Quoting IKE:


Have you seen the dry air heading into it...not sure about 99L....Link


I posted some of that imagery last night when the convection was disappearing. The key to this IMO is that 99L cannot fight off both the dry air and shear. One or other have to let up for it to stand a chance. The dry air is not going away any time soon but if the high centers overhead the system it would allow it to build some convection over the core and potentially hold the dry air at bay.

I guess we will just have to wait and see how this plays out. Not looking too good right now and a lot worse than 8 this morning when it seemed close to being classified.
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Quoting kmanislander:


The HH data makes it clear what pressures are out there.
ok, Now I see it. I also see 1011mb too.
Member Since: June 13, 2009 Posts: 0 Comments: 6881
Quoting IKE:


Have you seen the dry air heading into it...not sure about 99L....Link

Yep...that's a detriment alright
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Quoting scott39:
why does tropical atlantic has 1007mb if its 1010mb?


The HH data makes it clear what pressures are out there.
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Quoting FLstormwarning:


Here's your answer and that's one way NE no matter if this exits off the Yucatan or goes thru the Channel. To say this doesn't hit FL if this gets in the gulf now that's foolish. No ridge at all but light shear which is why the HWRF and GFDL maintain a cat. 3 or 4 storm in the gulf.


http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/fp0_180.shtml

The anticipated mid-level ridge is supposed to set up over FL as early as Friday and then slowly strengthen...and I think that (though not exclusively) will contribute to helping it steer away from the 'splitting the gap' scenario near the Yucatan.
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94. IKE
Quoting kmanislander:


Very much so. An abundance of West winds but pressures all showing near 1011 mbs. No TD for at least 12 to 18 hours unless something dramatic happens this afternoon with the convection. Until that can build over the center and drive the surface pressure down it is status quo or further weakening on the cards.


Have you seen the dry air heading into it...not sure about 99L....Link
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why does tropical atlantic has 1007mb if its 1010mb?
Member Since: June 13, 2009 Posts: 0 Comments: 6881
Quoting IKE:
17.4N and 82.4W....

1010.7 mb
(~ 29.85 inHg)


System has weakened.


Very much so. An abundance of West winds but pressures all showing near 1011 mbs. No TD for at least 12 to 18 hours unless something dramatic happens this afternoon with the convection. Until that can build over the center and drive the surface pressure down it is status quo or further weakening on the cards.
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GFS is best model to go by right now... especially since the ECMWF has almost nothing also. I would skip the GFDL, and HRWF right now until anything becomes a TS or pressure under 1005mbs.
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Quoting cat5hurricane:

This loop seems to favor a track getting close to FL with negates any ridging that would normally keep the inclement weather away. I just don't see this thing getting anywhere near FL. Not saying Floridians by any means should not monitor this but just don't see them under the gun with this particular system.


Here's your answer and that's one way NE no matter if this exits off the Yucatan or goes thru the Channel. To say this doesn't hit FL if this gets in the gulf now that's foolish. No ridge at all but light shear which is why the HWRF and GFDL maintain a cat. 3 or 4 storm in the gulf.


http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/fp0_180.shtml
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It should be no suprise that 99L is not developing that quickly right now. Thursday and Friday we will probably see something.
Member Since: June 13, 2009 Posts: 0 Comments: 6881
88. IKE
17.4N and 82.4W....

1010.7 mb
(~ 29.85 inHg)


System has weakened.
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Quoting cat5hurricane:

Sure hope it continues to not organize. I'm sure you guys down there in Cayman probably got enough rain out of this.


Rain is one thing, and yes we have had enough of that, but a strengthening system on your door step is not we need at all. Apart from the potential for loss and damage, trying to prepare in torrential rain with little lead time is itself a dangerous proposition.
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Quoting kmanislander:


Starting to look that way and the circulation is lookking a bit ragged, not as tight as a couple of hours ago. If the shear relaxes some, and there are signs that may be happening, it would likely recover fairly quickly.

Sure hope it continues to not organize. I'm sure you guys down there in Cayman probably got enough rain out of this.
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Quoting KennyNebraska:
Hey PensacolaDoug! :)

Is it too soon to know anything for certain about 99L and its future?

WTH is that one model showing it as a Cat 4 in the Gulf? That cannot be right, can it?



Hard for me to get very excited about it while that dry air is pushing towards it so strongly.
GFDL and HWF always seem to have a spin-up bias. Can't be ruled out tho. Too soon to make anything more than just a guess as to it's potential impact. If I lived on the sw Florida coast, I'd pay attention but I wouldn't be having "Charlie" or "Wilma" flashbacks just yet.
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Quoting scottsvb:
Pressure is about 1010mbs


Starting to look that way and the circulation is looking a bit ragged, not as tight as a couple of hours ago. If the shear relaxes some, and there are signs that may be happening, it would likely recover fairly quickly.
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Tropical Atlantic has pressure at 1007mb
Member Since: June 13, 2009 Posts: 0 Comments: 6881
Tropical Atlantic has 99L moving ESE at 4mph.
Member Since: June 13, 2009 Posts: 0 Comments: 6881

Again , true to an area where Sofla should watch .
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Looks like HH just made first pass through system center. Interesting to see what they report back when finished
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Pressure is about 1010mbs
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Quoting IKE:
17.7N and 82.4W...

1010.6 mb
(~ 29.84 inHg)


yeah, and that is in the NE quad very close to the center. This thing may not have a surface pressure below 1009 mbs.
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Quoting scooster67:
OMG! We have clouds over North Florida. Havn't had clouds in 2 weeks +. Change is a commin and I aint talking about Obama's kind of change!


LOL
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75. IKE
17.7N and 82.4W...

1010.6 mb
(~ 29.84 inHg)
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Quoting PRweathercenter:
If you'll notice in the past few hours invest 99 has been moving ESE, i wonder how long that pattern will last



it looks like it is making it's loop-de-loop.
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Quoting PRweathercenter:
If you'll notice in the past few hours invest 99 has been moving ESE, i wonder how long that pattern will last


It will last until it changes.
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Not Wishcasting, but we could use some rain up here in North Florida (Gainesville). If the GFDL holds true, we just might get some. Maybe more than we want though.
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Good day again

The high to the South of 99L that has been shearing it off from the SW has now moved to a position that is almost overhead the system. This should allow for more favourable conditions for development and that may come before tomorrow as currently suggested.

The 850 vort is well defined and the slow drift of the system is allowing the high to catch up to it. In addition, the rotation of 99L will also aid in establishing the anticyclone overhead so that would be the next thing to watch for IMO.
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WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1045 AM EDT WED 20 OCTOBER 2010
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 21/1100Z TO 22/1100Z OCTOBER 2010
TCPOD NUMBER.....10-141

I. ATLANTIC REQUIREMENTS
1. SUSPECT AREA (WESTERN CARIBBEAN)
FLIGHT ONE -- TEAL 70
A. 21/1200Z
B. AFXXX 0419A CYCLONE
C. 21/0800Z
D. 17.6N 81.5W
E. 21/1130Z TO 21/1530Z
F. SFC TO 15,000 FT

FLIGHT TWO -- TEAL 71
A. 22/0000Z
B. AFXXX 0519A CYCLONE
C. 21/2000Z
D. 17.6N 81.5W
E. 21/2330Z TO 22/0330Z
F. SFC TO 15,000 FT

2. SUCCEEDING DAY OUTLOOK:
A. CONTINUE 12-HRLY FIXES IF SYSTEM DEVELOPS
AND IS A THREAT.
B. POSSIBLE BUOY DEPLOYMENT MISSION FOR 22/1400Z.
3. REMARK: THE FIX MISSION FOR 20/1200Z IN TCPOD 10-140
WAS CHANGED TO A 20/1500Z INVEST MISSION.
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Try to compare pre-richard with the 4th tropical cyclone of the 2010 pacific typhoon season:

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Quoting reedzone:


Eventually in time, this system will go north, get pulled by a trough. The big question will be how strong it will be.


Really doesn't even need a trough, imo.

It will want to ride the western periphery of that ridge, wanting to go N and E the whole time.

A strong trough would just "shoot" it more to the E with a sharper turn than would otherwise be the case.

Member Since: September 9, 2008 Posts: 6 Comments: 3414
NW QUAD

Somewhat close to the center

1011.4 mb
(~ 29.87 inHg)
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting scooster67:

This looks good for Hong Kong and other area's of China. Cat 1-2 and not a 4-5

Yep. Not too mention Hong Kong will not be in the storm's dreaded right side...which should also lessen the impacts on the expected surge.
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NW QUAD

14:24:30Z 18.800N 83.550W

SFMR

27 knots
(~ 31.0 mph)
Member Since: January 30, 2010 Posts: 0 Comments: 3259
If you'll notice in the past few hours invest 99 has been moving ESE, i wonder how long that pattern will last
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Quoting cat5hurricane:
At least a better scenario for Hong Kong based on the track chance since this time yesterday.


This looks good for Hong Kong and other area's of China. Cat 1-2 and not a 4-5
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Quoting Seastep:


Way to early to say, but believe it is definitely a possibility if it forms and stays down there and then starts heading W, being near the Yucatan in 5 days. Only one way for it to go, really.



Eventually in time, this system will go north, get pulled by a trough. The big question will be how strong it will be.
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OMG! We have clouds over North Florida. Havn't had clouds in 2 weeks +. Change is a commin and I aint talking about Obama's kind of change!
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Quoting cat5hurricane:

This loop seems to favor a track getting close to FL with negates any ridging that would normally keep the inclement weather away. I just don't see this thing getting anywhere near FL. Not saying FL by any means is in the clear but just don't see them under the gun with this particular system.


Way to early to say, but believe it is definitely a possibility if it forms and stays down there and then starts heading W, being near the Yucatan in 5 days. Only one way for it to go, really.

Member Since: September 9, 2008 Posts: 6 Comments: 3414
Back in a bit... have to pretend to be at work. I will keep the HH data updated.






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Quoting jiminceiba:
the thing i find interesting...is that the blob isn't the hurricane in making..at least my thinking...correct me if i am wrong, but just to the sw of the blob is where the actual low is...and few clouds around it...but if you look at the visible loop...it has serious rotation...and in my limited knowlede..i would think that if that thing starts to get moisture from the blob...it will become the storm...please..i am new at this...am i correct?
your right!
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Tampaspin showed the map of the Atlantic showing how strong a Hurricane, despite shear and other factors, can be due to the TCHP and SSTs. A Major can still survive in the GOM if shear and other factors were not an issue. Gonna have to see how this all plays out. The GFDL and HWRF looks to keep the anticyclone over the storm all the way through the GOM, if that actually happens, then the strength of the storm is not surprising since temps and TCHP supports a major Hurricane.
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Quoting Neapolitan:
I would strongly disagree:

Click for larger image:

Appropriate tropical weather-related image


If the XTRP says it's a major, then I'll believe it :)

The cooler water and dry air should prevent a major hurricane in the gulf.

But I've been wrong before. Twice, in fact. :)
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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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