99L a threat to develop; damage from Typhoon Megi still largely unknown

By: Dr. Jeff Masters , 1:38 PM GMT on October 19, 2010

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Heavy thunderstorm activity has increased and grown more organized this morning over the southwestern Caribbean between Honduras and the Cayman Islands, in association with a tropical disturbance (Invest 99L). The storm is bringing heavy rain to the Cayman Islands; two inches has fallen so far this morning at Savannah on Grand Cayman Island. Recent satellite imagery shows that 99L has some rotation, and the winds on the northeast coast of Honduras at Puerto Lempira have shifted to the west-northwest, implying that 99L may be developing a surface circulation. Wind shear is a moderate 10 - 20 knots, which is low enough to allow some slow development. Water vapor satellite loops reveal that the atmosphere in the Western Caribbean is moist enough to support development, and the waters beneath are plenty warm, at 29°C. The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will mostly remain in the moderate range, 10 - 20 knots, for the remainder of the week. The current north-northwest motion of 99L should continue until Wednesday, when a strong ridge of high pressure is forecast to build in, forcing 99L to the south or west. However, steering currents will be weak Wednesday through Friday, making it difficult to predict where 99L may wander to. The only models that develop 99L are the GFDL and HWRF. The GFDL model predicts that 99L will spend enough time over water to develop into a hurricane, and brings the storm to the coast of Mexico's Yucatan Peninsula on Sunday morning. The HWRF model has 99L making landfall over Honduras late this week, before the storm has a chance to develop into a hurricane. NHC is giving 99L a 40% chance of developing into a tropical depression by Thursday. I believe the odds are higher, near 60%. The Hurricane Hunters are on call to investigate 99L this afternoon.


Figure 1. Morning satellite image of Invest 99L.

Damage from Super Typhoon Megi still largely unknown
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 extent of the destruction wrought by the great storm is still largely unknown. Preliminary news reports indicate that at least 10 people died, and the northern Philippine province of Isabela suffered severe damage. 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. Baguio near the west coast of northern Luzon received 7.72" of rain from the storm, and many mountainous regions likely received over a foot of rain.


Figure 2. Rainfall rates in excess of 1 inch per hour (orange colors) were observed by the polar-orbiting F-18 satellite in association with Megi at 00:40 UTC October 19, 2010. Image credit: Navy Research Lab, Monterey.

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 built a formidable new eyewall. At the same time, 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 intensify into a very dangerous Category 4 storm by Thursday. 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 near 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.

"Daily Downpour" airing this afternoon
Our live Internet radio show, "Daily Downpour", will be airing today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. You can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml, and I'll be discussing the latest info on Invest 99L with hosts Shaun Tanner and Tim Roche.

Jeff Masters

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well, .....Not much convection, but some spin in this area...

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Quoting wunderkidcayman:
you guy also need to know that 99L is getting shear at 5-10 kt


What's the critical value of shear in kts when we say that tropical cyclone development is no longer possible. I do observe the shear, which I understand to be moderate, but not strong enough to prevent 99L from forming into a tropical cyclone (but no rapid intensification).
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you guy also need to know that 99L is getting shear at 5-10 kt
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Quoting CyclonicVoyage:


What trough?


Check out this water vapor loop of the entire North Atlantic Basin:

http://www.ssd.noaa.gov/goes/east/natl/flash-wv.html

During the loop, click on the HDW-H (upper-level wind vectors) check box and the Lat/Lon check boxes. There is a very massive upper trough across eastern North America between 100W and 70W longitude. This can be seen by the v-shape in the water vapor motions and the massive collection of HDW-H wind vectors. The massive trough is moving eastward.

Any standard upper trough in the westerlies has upper divergence on its east side, which reduces surface pressure below. As the upper trough's divergence overspreads the low-level ridge, the ridge will gradually weaken (erode). So, I am wondering how that low-level ridge will be strong enough to deflect 99L NW or WNW when the ridge is struggling due the massive trough over eastern N America.
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Seems like when 99L gets trapped between those two converging DA masses, it will stall and develop.....

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Quoting NCHurricane2009:


The ridge has had some eastward displacement as the trough has knocked it somewhat. Yeah, 99L will go east, but it seems then it'll turn NE into E Cuba and then E Bahamas.


What trough?
Member Since: January 30, 2010 Posts: 0 Comments: 3259
invest 99l looking better then the yankees are!!!!hahaha,.,
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Quoting NCHurricane2009:


The ridge has had some eastward displacement as the trough has knocked it somewhat. Yeah, 99L will go east, but it seems then it'll turn NE into E Cuba and then E Bahamas.


To clarify, I mean that the ridge will turn the track from E to NE, which would then send it into E Cuba and E Bahamas. I don't see how those ridge countours suggest it'll go E, then turn NW or even W toward the Yucatan. This ridge is simply not shaped to turn this thing to the NW or W.
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Quoting CyclonicVoyage:


99L has room to move east until hitting the ridge to the east.



The ridge has had some eastward displacement as the trough has knocked it somewhat. Yeah, 99L will go east, but it seems then it'll turn NE into E Cuba and then E Bahamas.
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Quoting ParanoidAndroid:
Is that apparent eastward motion real or just the optical illusion created by shear?


Its moving eastward. Check out this shortwave IR sat. loop:

http://www.ssd.noaa.gov/goes/flt/t1/flash-ir2.html

Notice that the black clouds are the low-level clouds, and the blueish clouds are the higher cloud tops. If this thing was stationary with shear giving the illusion of an eastward motion, you would see a distinct swirl of black clouds seperating from the blue clouds as the sheared-off blue clouds leave the black swirl behind.

But with 99L, both the black cloud spin and the blue cloud spin are moving in tandem to the east-northeast.
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Quoting NCHurricane2009:


I don't know how the models see things evolving. The Yuctan? What! This thing is screaming east-northeastward right now with a very obvious trough over the eastern US steering it. This is not going to go west anytime soon, looks more like eastern Cuba/Jamaica to me.


99L has room to move east until hitting the ridge to the east.

Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting scooster67:
Pinball! 99L is the Ball and the HP areas are the bumpers. The troth is that spot you keep trying to bump the ball into.

Need the rain in North Florida, but not wishing for a major.


But the trough is eroding away the ridge to 99L's northeast, so it doesn't look like it'll go that far north. Sorry, don't see this bringing much help with the lack of rain in FL. Yeah the ridge might help with some northward deflection in track, but not that far north.
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Two models now develop 99L
GFDL leaves it between Yucatan & Cuba




HWRF sends it to Yucatan


While CMC puts it as a Low in the Gom and presents 2 systems one S of PR and another in the CAT


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Quoting HurricaneDean07:
Nite all

G'night!
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Is that apparent eastward motion real or just the optical illusion created by shear?
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Pinball! 99L is the Ball and the HP areas are the bumpers. The troth is that spot you keep trying to bump the ball into.

Need the rain in North Florida, but not wishing for a major.
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Quoting sunlinepr:


Excelent analysis


Thanks for the comment. Feeling good about that analysis.
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If you count Otto, we have had Matthew, Nicole, Otto, Paula form in the Caribbean region. If 99L pulls off this stunt, it'll be the FIFTH tropical cyclone in a row to form in the Caribbean region. Wow!
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Quoting NCHurricane2009:
Good early morning here just after midnight,

Hot off the press, my full history of 99L from its birth till right now (so you can see its origins), followed by some predictions!


Excelent analysis
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Nite all
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Quoting CyclonicVoyage:


Given the time frame that is rather consistent.


I don't know how the models see things evolving. The Yuctan? What! This thing is screaming east-northeastward right now with a very obvious trough over the eastern US steering it. This is not going to go west anytime soon, looks more like eastern Cuba/Jamaica to me.
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Quoting JLPR2:
So is 99L shrinking?
Seems to be concentrating on a smaller area, maybe Paula's cousin? XD

it's consolidationg, shrinking, and will be able to intensify faster due to it's size, it will be a td at the 5 am or a special advisory will be issued in the next hour or two.
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Quoting sunlinepr:


But the real is that Dry Air and shear are moving it somehow away from Yucatan...



That is actually the subtropical jet-stream.



Member Since: January 30, 2010 Posts: 0 Comments: 3259
I say we have a TD at 11 tomorrow morning.
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Good early morning here just after midnight,

Hot off the press, my full history of 99L from its birth till right now (so you can see its origins), followed by some predictions!
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1000. KEEPEROFTHEGATE (Mod)
POSS T.C.F.A.
XX/XX/99L
MARK
17.68N/81.93W
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Quoting shikori:

now has it going for the Yucatan


Given the time frame that is rather consistent.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting shikori:
where is the 11:00 o' clock advisory?

The National Hurricane Center only updates Tropical Depressions and up at 11 PM EDT, 5 AM EDT, 11 AM & 5 PM.

All other developing systems get updates at 2 PM, 8 PM, 2 AM & 8 AM under the Tropical Weather Outlook (TWO) tab :O)
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Quoting shikori:

now has it going for the Yucatan


But the real is that Dry Air and shear are moving it somehow away from Yucatan... Though there is DA arriving from the SE

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now has it going for the Yucatan
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..
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Cuba's Radar....

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Quoting SouthDadeFish:
Okay first of all the GFDL is not showing a cat 5. Those winds are 35m above the surface. It's showing a cat 4. Second, the GFDL is notorious for overdoing intensity forecasts, especially in this area. A cat five is incredibly unlikely at this time. Just as the NHC says, conditions are only marginally favorable. There is a 30% chance that this never becomes a tropical cyclone still. A large area of dry air is pushing in from the NW and it is clearly being felt. However, 99L has recently fired deeper convection closer to the center, which may be the kick start it needed.


Ayyy Captain. Which way shall we be goin'?

The who's it's and what ways were showing Richard looming at the surface in great numbers this afternoon.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Are winds going up for any weather stations in cayman?
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where is the 11:00 o' clock advisory?
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I think the camel is trying to sneak its nose under the edge of the tent.

256km radar for Hong Kong Observatory
and no official standby signal for a typhoon! (i.e. not even a hurricane watch posted yet)

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988. JLPR2
So is 99L shrinking?
Seems to be concentrating on a smaller area, maybe Paula's cousin? XD

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I dont think 99L is at 83.4W. More between 81.5W and 82.0W. IMO
Member Since: June 13, 2009 Posts: 0 Comments: 6912
Okay first of all the GFDL is not showing a cat 5. Those winds are 35m above the surface. It's showing a cat 4. Second, the GFDL is notorious for overdoing intensity forecasts, especially in this area. A cat five is incredibly unlikely at this time. Just as the NHC says, conditions are only marginally favorable. There is a 30% chance that this never becomes a tropical cyclone still. A large area of dry air is pushing in from the NW and it is clearly being felt. However, 99L has recently fired deeper convection closer to the center, which may be the kick start it needed.
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5 + days touring the Caribbean can do wonders for an ailing storm. However, it eventually has to go somewhere and climatology says N to varying degrees.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting AEKDB1990:
Lenny was another strange one. Paloma and Omar were other strange storms that blew up and fell apart really fast.
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I never speculate on intensity. I've seen it all and grown to know to expect it all. Things can and do change in a heartbeat and a heck of a lot faster than these maps & models update. A Cat 5 would not surprise me in the least. We're currently 5 days away from that forecast, highly speculative, and it's not the first time the GFDL showed it either.

Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting wunderkidcayman:
That is what I am going to hear from my teacher friend(Richard) "yes no school!"


LOL how ironic.
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That is what I am going to hear from my teacher friend(Richard) "yes no school!"
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Quoting wunderkidcayman:
that means bad news for us kmanhurricaneman huh well I say this Tomorrow morning we will have either TD 19 or very weak TS Richard TS warning will be up for us and maybe schools and businesses close anyway I am off for now


No skewl YES
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ok, i see didnt quite get it before.
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that means bad news for us kmanhurricaneman huh well I say this Tomorrow morning we will have either TD 19 or very weak TS Richard TS warning will be up for us and maybe schools and businesses close anyway I am off for now
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intensity i am in disagreement with however forcast tracking is good.
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Quoting kmanhurricaneman:
??????????


Apparently You and I are on the same page. We almost typed the same thing.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting CyclonicVoyage:
LOL at #970


what did 970 do
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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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