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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Quoting ackee:
it will be intresting to see what NHC say at 8am


If this is not at least TD then I have not learned anything after watching this blog for such a long time - LOL.
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Quoting IKE:
Looks like 20+ knots of WSW shear affecting 99L....at the coordinates of 18N and 83W...

lets hope it continues
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1119. KEEPEROFTHEGATE (Mod)
ALERT ATCF MIL 99X XXX 101019180000
2010101918
17.4 276.6
20.7 276.0
100
17.4 276.6
200000
1010200000
1
WTNT21 KNGU 200000
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/1. FORMATION OF A TROPICAL CYCLONE IS POSSIBLE WITHIN 100 NM EITHER
SIDE OF A LINE FROM 17.5N 83.5W TO 20.8N 84.0W OVER THE NEXT 24 HOURS.
AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF A NUMBERED TROPICAL CYCLONE
WARNING AT THIS TIME.
2. REMARKS: CURRENT MODEL GUIDANCE IS DEPICTING GRADUAL INTENSIFICATION
OF A LOW SITUATED OVER THE NORTHWESTERN CARIBBEAN. THIS SYSTEM IS MOVING
NORTH AT APPROXIMATELY 9 KNOTS. THIS SYSTEM IS CENTERED OVER WARM
SEA SURFACE TEMPERATURES OF 85 TO 90 DEGREES FAHRENHEIT, WEAK VERTICAL
WIND SHEAR, AND UNDER THE WESTERN PORTION OF AN UPPER LEVEL ANTICYCLONE
WHICH SHOULD HELP TO ENHANCE THE DEVELOPMENT OF THIS TROPICAL FEATURE.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR ALLOWED TO
EXPIRE BY 210000Z.//

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Quoting shikori:
JGHS
My grandson is at CHHS and both of them flood bad.
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1115. scott39
99L is not at 82.9W anymore. Its farther E IMO.
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Quoting shikori:


Like last time. This is why I am calling my buddy to bring back my game to school today.
Where do you go to school ?
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Quoting IKE:
Looks like 20+ knots of WSW shear affecting 99L....at the coordinates of 18N and 83W...



And 99L continues to slowly organize.
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1112. scott39
99L is moving ENE in the short term just like the GFDL and HWRF are forecasting. It will then be pushed back to the WNW and NW later.
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Quoting ackee:
it will be intresting to see what NHC say at 8am
I am wondering what the update here is going to say. All the schools have flooding issues but the next update is at 7 am local time and the school bus picks up the kids in the Eastern districts around 6:30 so I guess they will go for the trip to be sent back home. LOL
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1109. ackee
it will be intresting to see what NHC say at 8am
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1108. ackee
Quoting CaribbeanStorm:


News just in...a little boy washed away in a river in St. Cathering, Jamaica. Seems to be casualty number 1. The skies in Kingston looking ominous.
the sky look the here in ST.catherine
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Quoting shikori:
Stormwatcher what are the winds like outside. I cant depend on caymanchillin's weather station. It seems something is wrong with it's wind vane winds are 0mph and its saying the direction is NNW stil. How can you tall wind direction if there is no wind?
Gusts every once in a while maybe 15-20 mph but pretty calm right now. Heavy rain though.
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1104. IKE
Looks like 20+ knots of WSW shear affecting 99L....at the coordinates of 18N and 83W...

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1103. scott39
Goodmorning, Tropical Atlantic has 99L moving ENE. GFS and Euro are out to lunch and dinner on 99L! GFDL is looking more and more like the one to follow.
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Quoting CaribbeanStorm:


Yes, Gustav was not very nice to us.
Us either but I am thinking Paloma.
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Quoting CaribbeanStorm:


Yes, Gustav was not very nice to us.


News just in...a little boy washed away in a river in St. Cathering, Jamaica. Seems to be casualty number 1. The skies in Kingston looking ominous.
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1100. WxLogic
Good Morning...
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Quoting ackee:
I am noticeing the last few frames where 99L centre was located does seem like trying to relocate under the convection guess we see when when hurricane hunter go out there this may be another Gustav in the making


Yes, Gustav was not very nice to us.
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Quoting stormwatcherCI:
As a Cat 5.


The chanel, maybee, cat 5 me no think so! Everything has to be just WRONG for cat 5. 1 or 2 yea maybee,
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Quoting Autistic2:


That shows it hitting the "clear shot chanel" into the gulf?
As a Cat 5.
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1095. ackee
I am noticeing the last few frames where 99L centre was located does seem like trying to relocate under the convection guess we see when when hurricane hunter go out there this may be another Gustav in the making
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Quoting CaribbeanStorm:
If GFDL is correct I find this to be very interesting.

GFDL


That shows it hitting the "clear shot chanel" into the gulf?
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If GFDL is correct I find this to be very interesting.

GFDL
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Quoting IKE:
Center of 99L is completely exposed. Looks near 18N and 83W.

NHC is not going to upgrade a naked swirl.

ATCF placed the center at 17.8N/82.9W at 2:30 EDT; in the four hours since then, the center has moved even farther east. I think shear is getting close to exposing the CoC, but that hasn't actually happened yet, although visible images in the next hour will really tell the tale.
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How far north can 99 go. Been looking at the models one a day for a while. Bottom line. The models have nfi where 99 is going!
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Good Morning

A nice little tropical storm (not Hurricane) would be great for us here in NE Fl. That coud bring some rain even to the east fl coast, becoming a very dry place here. Dry = fires
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Finally someone else sees the OBVIOUS shear Ive meen mentioning since yesterday morning
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1087. IKE
Center of 99L is completely exposed. Looks near 18N and 83W.

NHC is not going to upgrade a naked swirl.
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GFDL is interesting Eastward movement predicted and currently happening. we will see if the exposed center slides back under the expanding convection. next 24hrs will be very very ket to the intensity or lack thereof
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Where is Pre-Richard's center? Could someone put a circle over it?
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GFDL went nuts with 99L.. makes it a borderline Category 5 going into the Gulf.
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1083. IKE
SYNOPSIS FOR CARIBBEAN SEA AND TROPICAL N ATLC FROM 07N TO 22N
BETWEEN 55W AND 65W
530 AM EDT WED OCT 20 2010

.SYNOPSIS...LOW PRES 1008 MB NEAR 18N83W WILL REMAIN NEARLY
STATIONARY THROUGH THU THEN DRIFT SW AND MOVE INTO CENTRAL
AMERICA NEAR THE BORDER OF HONDURAS AND NICARAGUA OVER THE
WEEKEND...POSSIBLY AS A TROPICAL CYCLONE.
.............................................

SYNOPSIS FOR THE GULF OF MEXICO
430 AM CDT WED OCT 20 2010

.SYNOPSIS...WEAK HIGH PRES ACROSS THE N GULF. THE HIGH WILL
STRENGTHEN OVER THE SE U.S. FRI COMBINED WITH LOWER PRES OVER
THE SOUTHERN PLAINS WILL INCREASE S WINDS OVER THE NW GULF FRI
THRUGH SUN.
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Quoting shikori:
GFDL is saying this already has TS winds, and since it has been right track wise and it might also seem intensity wise it will continue to move ne towards Jamaica while strengthening, before turning north then wnw spelling doom for Cayman if the intensity follows.


It seems to me that where this system is positioning itself it could do a lot of damage to the North Coast here in Jamaica before it turns wnw. It does not seem that the mountains here will hinder the development of Richard.
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1079. ackee
I think 99L will be upgraded at 11am to TD #19 the GFDL seem to be only model on taget with 99L
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I don't know how this hasn't been named yet I expect Richard at 11 am
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99L's rather small. That would explain why the models have done so poor on this system.
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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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