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 kmanislander:


Huh ??. On Grand Cayman ?
EE says NNW at 17 mph.
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If it develops, would it keep going NW crossing that Dry Air, shear region???

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Quoting kmanislander:


East to NE at 5 mph at my home on the SW side of the island. 1011.4 mbs

?? where is Shikori?
I am confused..
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I sure wish we were going to get some rain from 99 l. We sure could use it here in Sarasota Florida
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Quoting doorman79:


What are the models seeing that makes it do a circle? Very hostile conditions ahead. The anticyclone that is on top now should get torn apart by the front, right?


A ridge of high pressure that builds in over the GOM and forces the system South and then West
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Quoting kmanislander:


Yes, it is either drifting to the East or the convection is being sheared in that direction giving the impression of a due East drift.

Some seriously dry air pushing down from the NW though and undercutting the West and NW inflow to 99L. No surprise the system is struggling to generate any significant convection.



Been looking at IR2 for a bit and IMO, Eastward ho. Just west of the western tip of Grand Cayman, round 18N 82W IMO.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting shikori:
NNW 17 mph


Huh ??. On Grand Cayman ?
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Quoting shikori:
NNW 17 mph

hmmmm
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Quoting pottery:

Any south winds where you are?


East to NE at 5 mph at my home on the SW side of the island. 1011.4 mbs
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Dry Air from W / SE



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Quoting CyclonicVoyage:



Seems 99L will be right under you by morning?
Quoting CyclonicVoyage:



Seems 99L will be right under you by morning?
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Quoting kmanislander:


Yes, it is either drifting to the East or the convection is being sheared in that direction giving the impression of a due East drift.

Some seriously dry air pushing down from the NW though and undercutting the West and NW inflow to 99L. No surprise the system is struggling to generate any significant convection.



What are the models seeing that makes it do a circle? Very hostile conditions ahead. The anticyclone that is on top now should get torn apart by the front, right?
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Quoting AtHomeInTX:


Ah ok. Thanks. Haven't looked at the shear/steering maps lately. Weather has been just gorgeous. Other than the drought and fire danger doing ok here.

Unfortunately, the drought conditions may really become a problem over the next few mos:

Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting kmanislander:


Yes, it is either drifting to the East or the convection is being sheared in that direction giving the impression of a due East drift.

Some seriously dry air pushing down from the NW though and undercutting the West and NW inflow to 99L. No surprise the system is struggling to generate any significant convection.


Any south winds where you are?
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Quoting CyclonicVoyage:



Seems 99L will be right under you by morning?


Yes, it is either drifting to the East or the convection is being sheared in that direction giving the impression of a due East drift.

Some seriously dry air pushing down from the NW though and undercutting the West and NW inflow to 99L. No surprise the system is struggling to generate any significant convection.

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Quoting pottery:

Yep!!
There are a couple of individuals who dont know if they are going to bed or not!
99L is simple...


I just got here! dang nabbit!
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Quoting CyclonicVoyage:
Seems like 99L has suddenly become well organized when compare to the blog.

Yep!!
There are a couple of individuals who dont know if they are going to bed or not!
99L is simple...
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Quoting kmanislander:


Wow, now I am mixed up LOL



Seems 99L will be right under you by morning?
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting pottery:

You noticed I left out the 'W' ???
heheheh


Thats just wrong lol
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Quoting doorman79:


There you go stirring the pot!! :)

Looks like we are gonna get a little rain in the next hour or so! I have been waiting to plant. Kman, what you thinking on 99l?

You noticed I left out the 'W' ???
heheheh
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Quoting aspectre:
Invest 99L
18Oct 12amGMT - 13.3n81.0w - 20knots - 1010mb - *12.6n80.6w*13.1n81.0w*13.4n81.1w*13.4n81.0w
18Oct 06amGMT - 13.7n81.4w - 20knots - 1010mb - ATCF*14.0n81.8w*14.3n81.8w*13.8n81.5w
18Oct 12pmGMT - 14.1n81.8w - 25knots - 1010mb - ATCF*15.1n82.5w*15.0n82.4w*14.1n81.9w
18Oct 06pmGMT - 14.6n82.3w - 25knots - 1010mb - ATCF*15.7n83.2w*14.5n82.2w
19Oct 12amGMT - 15.3n82.8w - 25knots - 1009mb - ATCF*15.0n82.6w*15.1n82.7w
19Oct 06amGMT - 16.0n83.1w - 25knots - 1009mb - ATCF*15.7n83.0w*1008mb*15.8n82.9w
19Oct 12pmGMT - 16.7n83.3w - 25knots - 1009mb - ATCF*16.5n83.3w*1008mb*16.5n83.0w
19Oct 06pmGMT - 17.4n83.4w - 30knots - 1008mb - ATCF*17.0n83.0w*1009mb
20Oct 12amGMT - 17.6n83.4w - 30knots - 1009mb - ATCF
* Before NHC reevaluated&revised the ATCF numbers
20knots=~37km/h _ 25knots=46.3km/h _ 30knots=~55.6km/h

Copy&paste 13.3n81.0w, 13.7n81.4w, 14.1n81.8w, 14.6n82.3w, 15.3n82.8w-16.0n83.1w, 16.0n83.1w-16.7n83.3w, 16.7n83.3w-17.4n83.4w, 17.4n83.4w-17.6n83.4w, ctm, cyo into the GreatCircleMapper for a look at the last 24^hours


Member Since: August 25, 2009 Posts: 20 Comments: 6785
Seems like 99L has suddenly become well organized when compare to the blog.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting pottery:

I thought he meant 'bad' as in "Bad Storm.."


There you go stirring the pot!! :)

Looks like we are gonna get a little rain in the next hour or so! I have been waiting to plant. Kman, what you thinking on 99l?
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Quoting KerryInNOLA:
2010 shall be known as the season of the fish, since no hurricane struck solid land

LOL
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Quoting KerryInNOLA:
2010 shall be known as the season of the fish, since no hurricane struck solid land


I believe you mean the CONUS?
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Quoting CyclonicVoyage:


Why is that a bad forecast? That is exactly where the weakness is to develop?


Bad forecast for Conus / FL -wish for the end of the season....though it's still october....
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Quoting stormwatcherCI:
No, I said good night to weatherlover94 and you said see you tomorrow to me. Looks like we are just as confused as 99L. LOL


Wow, now I am mixed up LOL
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Quoting kmanislander:


LOL, no. I said "see you tomorrow" to Stormwatcher who was leaving !
No, I said good night to weatherlover94 and you said see you tomorrow to me. Looks like we are just as confused as 99L. LOL
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Quoting pottery:

I thought he meant 'bad' as in "Bad Storm.."


My apologies if that is the case.

130kts, yeah that's bad. GFDL has been stuck on that for a couple days now.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting pottery:

I thought he meant 'bad' as in "Bad Storm.."
That's what I thought too as in bad for the GOM.
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Quoting CyclonicVoyage:


I thought you were leaving, lol. Sorry, thanks for the info. Have a good night. Mid October leans my mind to a trough but, we'll see.


LOL, no. I said "see you tomorrow" to Stormwatcher who was leaving !
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Quoting shikori:
That's old. This is from early afternoon.
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Quoting CyclonicVoyage:


Why is that a bad forecast? That is exactly where the weakness is to develop?

I thought he meant 'bad' as in "Bad Storm.."
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Quoting kmanislander:


Yes, that type of set up has been coming and going now for the past two days where you get a COL developing between two ridges leaving a weakness in between. That would prevent whatever 99L becomes from being drawn out to the N across Cuba. Eventually one of two things will happen. Either a trough would dig down and pull it out or a high would build in and force it to the South and then West towards the Yucatan.

Too difficult to call this far out.


I thought you were leaving, lol. Sorry, thanks for the info. Have a good night. Mid October leans my mind to a trough but, we'll see.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
ok wishcasters....prove me wrong...low has 70 % chance of developing but the easterly steering winds to the north will block a CONUS hit especially Florida...so no worries for us...as stated on the WEATHER CHANNEL TROPICAL UPDATE...at 9:50 PM...Thoughts to the contrary???
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Quoting sunlinepr:
Bad forecast, develops 99L and sends it to the Gom...



Why is that a bad forecast? That is exactly where the weakness is to develop?
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting CyclonicVoyage:


Looking at the map from CIMMS, are we not looking at this very scenario that is supposed to persist?

AT 500 HPA THE RIDGE WILL SPLIT IN TWO CELLS...THE
AFOREMENTIONED ONE OVER MEXICO/WESTERN GULF AND A NEW ONE ACROSS
THE EASTERN CARIBBEAN-CENTRAL ATLANTIC. THIS WILL FAVOR A WEAKNESS
IN THE HEIGHT FIELD ACROSS THE NORTHWESTERN CARIBBEAN BY THE END
OF THE FORECAST CYCLE.


Yes, that type of set up has been coming and going now for the past two days where you get a COL developing between two ridges leaving a weakness in between. That would prevent whatever 99L becomes from being drawn out to the N across Cuba. Eventually one of two things will happen. Either a trough would dig down and pull it out or a high would build in and force it to the South and then West towards the Yucatan.

Too difficult to call this far out.
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Bad forecast, develops 99L and sends it to the Gom...

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Quoting pottery:

Hope you are wrong again!
A storm would be nice to look at and track. But where it is, if it develops into anything big, someone is going to get hit... guarantee that!

I honestly hope so, anyways, we'll see soon enough, checking out for the night, everyone have a good one!
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Quoting stormpetrol:

Within 24 hours , I think we'll all be singing a different tune, with a potentially dangerous systems in our neck of the woods, not an alarmist, just a realist on what I've seen happen before! Hopefully I'm wrong, 2 nights of successive crow is enough for me, but 3 wouldn't hurt if I'm wrong again , once we keep safe!


This could become a dangerous system, no doubt about that, but a lot would have to happen for that to come about in 24 hours. Have you looked at the shear tendency map ?.

Rising shear on all sides of 99L now and dry air pressing in. Conditions are marginal at best for this to develop quickly.
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00Z MSLP map is interesting too.

The prior one was 1010mb like the 1014mb line on the chart below, just N of the center.

Anyone know how to get archived frames from PSU e-Wall?

Member Since: September 9, 2008 Posts: 6 Comments: 3414
Quoting kmanislander:


The GFDL run is over a much longer time frame than the steering I just posted which is a short term 3 hour map. My point was that until the GFDL has a classified system to run with it is very unreliable.


Looking at the map from CIMMS, are we not looking at this very scenario that is supposed to persist?

AT 500 HPA THE RIDGE WILL SPLIT IN TWO CELLS...THE
AFOREMENTIONED ONE OVER MEXICO/WESTERN GULF AND A NEW ONE ACROSS
THE EASTERN CARIBBEAN-CENTRAL ATLANTIC. THIS WILL FAVOR A WEAKNESS
IN THE HEIGHT FIELD ACROSS THE NORTHWESTERN CARIBBEAN BY THE END
OF THE FORECAST CYCLE.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting stormpetrol:

Within 24 hours , I think we'll all be singing a different tune, with a potentially dangerous systems in our neck of the woods, not an alarmist, just a realist on what I've seen happen before! Hopefully I'm wrong, 2 nights of successive crow is enough for me, but 3 wouldn't hurt if I'm wrong again , once we keep safe!

Hope you are wrong again!
A storm would be nice to look at and track. But where it is, if it develops into anything big, someone is going to get hit... guarantee that!
Member Since: Posts: Comments:
Invest 99L
18Oct 12amGMT - 13.3n81.0w - 20knots - 1010mb - *12.6n80.6w*13.1n81.0w*13.4n81.1w*13.4n81.0w
18Oct 06amGMT - 13.7n81.4w - 20knots - 1010mb - ATCF*14.0n81.8w*14.3n81.8w*13.8n81.5w
18Oct 12pmGMT - 14.1n81.8w - 25knots - 1010mb - ATCF*15.1n82.5w*15.0n82.4w*14.1n81.9w
18Oct 06pmGMT - 14.6n82.3w - 25knots - 1010mb - ATCF*15.7n83.2w*14.5n82.2w
19Oct 12amGMT - 15.3n82.8w - 25knots - 1009mb - ATCF*15.0n82.6w*15.1n82.7w
19Oct 06amGMT - 16.0n83.1w - 25knots - 1009mb - ATCF*15.7n83.0w*1008mb*15.8n82.9w
19Oct 12pmGMT - 16.7n83.3w - 25knots - 1009mb - ATCF*16.5n83.3w*1008mb*16.5n83.0w
19Oct 06pmGMT - 17.4n83.4w - 30knots - 1008mb - ATCF*17.0n83.0w*1009mb
20Oct 12amGMT - 17.6n83.4w - 30knots - 1009mb - ATCF
* Before NHC reevaluated&revised the ATCF numbers
20knots=~37km/h _ 25knots=46.3km/h _ 30knots=~55.6km/h

Copy&paste 13.3n81.0w, 13.7n81.4w, 14.1n81.8w, 14.6n82.3w, 15.3n82.8w-16.0n83.1w, 16.0n83.1w-16.7n83.3w, 16.7n83.3w-17.4n83.4w, 17.4n83.4w-17.6n83.4w, ctm, cyo into the GreatCircleMapper for a look at the last 24^hours
Member Since: August 21, 2007 Posts: 0 Comments: 4860

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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.