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 BLee2333:
would you consider it a TD with this?

"BEST WINDSHIFT CENTER WAS AT 19:05:50Z AT 17 31N 83 35W"



It means that the winds shifted, as you would expect in a closed circulation.
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Quoting Goldenblack:
Forgive my ignorance, but I am assuming that tourism is probably the number 1 industry down there. All this tropical activity in the past two weeks must be hurting. Correct me if I am wrong.




Tourism and financial services are the twin pillars of our economy. Cruise tourism is the strongest portion of the tourism product right now and when we have bad weather the ships might either by pass us entirely or the number of passengers coming ashore is very limited.
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Bingo, doesn't it have to be sustained for 6 hours to attain TD by definition?

Quoting Seastep:


The concentrated thunderstorm activity is the kicker. Has everything else, really, but NHC likes to see that over the center.
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would you consider it a TD with this?

"BEST WINDSHIFT CENTER WAS AT 19:05:50Z AT 17 31N 83 35W"

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They rarely issue a vortex message and not upgrade, meaning they found a closed circulation and TD force winds.

IMO 99L's a 25kt Depression.
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Quoting bloodstar:
At this point, I can't imagine this will be a Tropical Depression at 5PM, the low is extremely broad and not very organized. In addition, there isn't a very well defined concentration of persistent thunderstorm activity. And while I'm sure there are cases where storms looked worse and were still designated a Tropical Depression, both factors above will probably keep it from designation.

If it has more thunderstorm activity, or the pressure gradient tightens up, it'll get designated IMO. It needs one or the other to happen first though.


The concentrated thunderstorm activity is the kicker. Has everything else, really, but NHC likes to see that over the center.
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Quoting pilotguy1:


Up yours. Jeez. Any opinion as long as it agrees with yours.


Flagged
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Agree, especially in the US, there is nothing solid yet stating that this will ever even get out of the Western Caribbean.

Quoting pilotguy1:


I agree. I just don't think anyone should get too excited at this point.
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 19th day of the month at 19:37Z
Corrected: This observation corrected a previous observation.
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Mission Purpose: Investigate eight suspect area (flight in the North Atlantic basin)
Mission Number: 1
Observation Number: 13
A. Time of Center Fix: 19th day of the month at 19:09:00Z
B. Center Fix Coordinates: 17°23'N 83°29'W (17.3833N 83.4833W)
B. Center Fix Location: 191 miles (308 km) to the SW (226°) from George Town, Cayman Islands (GBR).
C. Minimum Height at Standard Level: Not Available
D. Estimated (by SFMR or visually) Maximum Surface Wind: 27kts (~ 31.1mph)
E. Location of the Estimated Maximum Surface Wind: 20 nautical miles (23 statute miles) to the NNW (347°) of center fix
F. Maximum Flight Level Wind Inbound: From 112° at 20kts (From the ESE at ~ 23.0mph)
G. Location of Maximum Flight Level Wind Inbound: 21 nautical miles (24 statute miles) to the NNW (347°) of center fix
H. Minimum Sea Level Pressure: 1009mb (29.80 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 22°C (72°F) at a pressure alt. of 303m (994ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 23°C (73°F) at a pressure alt. of 302m (991ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 22°C (72°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind and Pressure
N. Fix Level: 1,500 feet
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 5 nautical miles
Remarks Section - Remarks That Were Decoded...
Maximum Flight Level Wind: 20kts (~ 23.0mph) in the north quadrant at 18:59:30Z
Maximum Flight Level Wind Outbound: 21kts (~ 24.2mph) in the southeast quadrant at 19:15:30Z
Sea Level Pressure Extrapolation From: Below 1,500 feet
Remarks Section - Additional Remarks...
BEST WINDSHIFT CENTER WAS AT 19:05:50Z AT 17 31N 83 35W
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting rmbjoe1954:
Is convection building around the COC?

Yes, as evidenced by both the RGB and Rainbow IR loops.
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Quoting bwi:
Interesting that the plane is flying around east of the reported center and still finding pressure right at 1009mb. Maybe when it turns back to the "center" it will find 1008?


That would be a good prediction.
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That is quite a change in vort since earlier..


Quoting Seastep:
18Z CIMSS charts are out. Everything starting to stack up around the 700mb vort. Organizing fairly quickly.

Upper level anti-cyclone continues to follow along, too.

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At this point, I can't imagine this will be a Tropical Depression at 5PM, the low is extremely broad and not very organized. In addition, there isn't a very well defined concentration of persistent thunderstorm activity. And while I'm sure there are cases where storms looked worse and were still designated a Tropical Depression, both factors above will probably keep it from designation.

If it has more thunderstorm activity, or the pressure gradient tightens up, it'll get designated IMO. It needs one or the other to happen first though.
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359. bwi
Interesting that the plane is flying around east of the reported center and still finding pressure right at 1009mb. Maybe when it turns back to the "center" it will find 1008?
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18Z CIMSS charts are out. Everything starting to stack up around the 700mb vort. Organizing fairly quickly.

Upper level anti-cyclone continues to follow along, too.

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Quoting pilotguy1:


With all due respect, or not. This thing is not very exciting so far.

Sorry the weather can't provide you the stimulation you crave. I suggest you write to Mother Nature immediately and demand a full refund!!!

;-)
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Quoting LightningCharmer:
Sounds like a corrupted file in the caché, cookie or script most likely. It would be too lengthy, off topic and a discourtesy to other bloggers to describe the remedy in this comment. WUMail, and I can pass on a tip or two.


problem solved...i just did a system restart...problem went away.....thanks for the advice though....
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I would have to think that we just need to give it time, like any other system, it is not going anywhere real fast.... I think those in the Caribbean western Cuba, Honduras, etc. might disagree with that analysis too

Quoting mcluvincane:


Then don't pay attention to it
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Is convection building around the COC?
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Quoting pilotguy1:


With all due respect, or not. This thing is not very exciting so far.


Then don't pay attention to it
Member Since: June 2, 2010 Posts: 0 Comments: 1390
Jeff, I don't know...there is a lot of variation between runs with the GFDL right now. Now that we have TD 19 (not confirmed totally), lets see what happens.

Quoting Jeff9641:
The GFDL nailed Wilma 5 years ago I wonder if the same is happening now!
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Forgive my ignorance, but I am assuming that tourism is probably the number 1 industry down there. All this tropical activity in the past two weeks must be hurting. Correct me if I am wrong.


Quoting kmanislander:


Even heavy rain days inflict a lot of economic damage for the duty free stores as the cruise lines have to tender people ashore and who wants to ride a tender from a ship and then walk around in the rain ?.
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It's interesting that the max surface wind was found some 20 miles to the NNW of the center fix position. Usually the max wind would be somewhere in the NE or SE quad. If this tightens up some in the next 6 hours the wind speed could ramp up fairly quickly in the eastern semi circle.
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I would not be surprised if this becomes a tropical storm by wednesday morning some time just by looking at the satellite images
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Quoting Neapolitan:

That's the upwelling caused by a recent Tehuano Event, a wind phenomenon (the Tehuantepecer) that can drop SSTs in the area by up to 10.C in a single day...

Click for larger image:

Appropriate tropical weather-related image
Thanks for the excellent link.
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Invest 99L
17Oct 06pmGMT - 12.8n80.4w - 20knots - 1009mb - ATCF*11.6n78.5w*12.3n79.9w*12.5n80.1w
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 - 15.1n82.7w - 25knots - 1009mb - ATCF*15.0n82.6w
19Oct 06amGMT - 15.8n82.9w - 25knots - 1009mb - ATCF*15.7n83.0w*1008mb
19Oct 12pmGMT - 16.5n83.0w - 25knots - 1009mb - ATCF*16.5n83.3w*1008mb
19Oct 06pmGMT - 17.0n83.0w - 30knots - 1009mb - ATCF
* Before NHC reevaluated&revised the ATCF numbers

Copy&paste 12.8n80.4w, 13.3n81.0w, 13.7n81.4w, 14.1n81.8w, 14.6n82.3w-15.1n82.7w, 15.1n82.7w-15.8n82.9w, 15.8n82.9w-16.5n83.0w, 16.5n83.0w-17.0n83.0w, ctm, cyo into the GreatCircleMapper for a look at the last 24^hours
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Quoting Goldenblack:
Yeah, agreed.

Looking back on my first post, I think the rain alone is enough to cause some issues, just seems like this one may be a real disruption to the CI for a lot of reasons.



Even heavy rain days inflict a lot of economic damage for the duty free stores as the cruise lines have to tender people ashore and who wants to ride a tender from a ship and then walk around in the rain ?.
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Quoting jiminceiba:
just tried restarting the browser..no effect...all other websites...no problem...just this website is doing it...i am using firefox...never had a problem before...i mean years...
Sounds like a corrupted file in the caché, cookie or script most likely. It would be too lengthy, off topic and a discourtesy to other bloggers to describe the remedy in this comment. WUMail, and I can pass on a tip or two.
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We have the rain event already going on here now. Totally socked in with low cloud deck
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Yeah, agreed.

Looking back on my first post, I think the rain alone is enough to cause some issues, just seems like this one may be a real disruption to the CI for a lot of reasons.

Quoting kmanislander:


What I have always been concerned about with this system is the potential for a slow crawl close to us then a stall. Over the past couple of days the steering has shown a propensity to collapse over the NW Caribbean in an area of very weak flow between us and the Yucatan.

My thinking was for this to possibly stall out very close to us, sit for some time and then get pushed back to the South by a building ridge of high pressure over the SE CONUS.

We will need to watch the evolution of the steering winds very carefully. October and November are well known for erratic track behaviour from tropical systems in the Caribbean.

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Quoting Neapolitan:

That's the upwelling caused by a recent Tehuano Event, a wind phenomenon (the Tehuantepecer) that can drop SSTs in the area by up to 10.C in a single day...

Click for larger image:

Appropriate tropical weather-related image


NICE! Thank you for the explanation! I saw that one too, and was clueless...
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337. bwi
HH found looks like 30kt surface wind out of the SW at about 17.2 north? Regardless of the pretty high pressures, that wind reading, if it's accurate and I'm interpreting correctly, is a concern.
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Quoting Goldenblack:
Hi Kman...aggressive description. do you think it has time to create more than rain event issues for you in the CI? (Given slow forecast speed?)



What I have always been concerned about with this system is the potential for a slow crawl close to us then a stall. Over the past couple of days the steering has shown a propensity to collapse over the NW Caribbean in an area of very weak flow between us and the Yucatan.

My thinking was for this to possibly stall out very close to us, sit for some time and then get pushed back to the South by a building ridge of high pressure over the SE CONUS.

We will need to watch the evolution of the steering winds very carefully. October and November are well known for erratic track behaviour from tropical systems in the Caribbean.

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Quoting kmanislander:


You must be prescient !. I was just about to post the data from that buoy. 99L starting to take on a different look now, more aggressive if I might put it that way.


LOL. Well, you know what they say...
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I watched a couple of mets on Accuweather. They say the most likely scenerio is thst 99L will do a loop and go back W. depending on how far it gets N will depend if it goes into CA or the Yucatan. They say it will more than likely miss the trough to the N to pull it NE. With it spending that much time over water and low wind shear, would more than likely produce at Cat2 or even Cat3 hurricane.
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Quoting Jeff9641:


He's actually right because a trough will be entering the C Gulf Coast at the time and a hard NE turn will occur similar to Charley. Levi32 if you watched his tidbit explains all of this. I've been explaing this as well since yesterday and I'm tired of repeating myself. Bottline this ULL in California could be problems for FL inregards to kicking this out to the NE and yes FL Looks to be in trouble come Monday or Tuesday next week.
Come on!! Trouble or just a nice rain event before the dry season sets in (that's assuming it heads to Floriduh)? Let's be realistic. Always be prepared but don't be overzealous!
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Hi Kman...aggressive description. do you think it has time to create more than rain event issues for you in the CI? (Given slow forecast speed?)

Quoting kmanislander:


You must be prescient !. I was just about to post the data from that buoy. 99L starting to take on a different look now, more aggressive if I might put it that way.
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So much for the euro and the gfs
Member Since: June 2, 2010 Posts: 0 Comments: 1390
Td has formed in the Caribbean
Member Since: June 2, 2010 Posts: 0 Comments: 1390
19:13:30Z 17.217N 83.300W

1009.2 mb
(~ 29.80 inHg)

30 knots
(~ 34.5 mph)
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Quoting CyclonicVoyage:
Vortex message says TD19 has formed.


Now we need a confirmation from ATCF and NHC and we are good to go.
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You are correct sir, we have a TD.....congrats all (its like a birth)

Quoting CyclonicVoyage:
Vortex message says TD19 has formed.
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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.