An Atlantic tropical wave worth watching

By: Dr. Jeff Masters , 2:46 PM GMT on October 04, 2009

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A large tropical wave near 9N 40W, midway between Africa and the Lesser Antilles Islands, is generating a considerable amount of heavy thunderstorm activity as it moves west to west-northwest at 15 mph. The wave is under about 10 - 15 knots of wind shear, and this morning's QuikSCAT pass showed a large and disorganized region of converging winds in the region, with top winds of 25 mph. There is very little dry air in the vicinity, and conditions appear favorable for some slow development of this wave. None of the computer models develop the wave, but they do show relatively low wind shear along the wave's path for the next five days. The wave should reach the Lesser Antilles Islands by Wednesday.


Figure 1. The large tropical wave in the middle Atlantic.

In the Philippines, Tropical Storm Parma continues to linger offshore the northern tip of the Philippines' Luzon Island, bringing heavy rain. The storm has been blamed for the deaths of 17 people in the Philippines, but has not not had the devastating impact that was earlier feared. Parma's heaviest rains will stay offshore of the Philippines today (Figure 2).


Figure 2. Forecast rain amounts for Parma for the 24-hour period ending at 06 UTC October 5 (2am EDT Monday). This forecast is based on satellite measurements of Parma's current rainfall rate, plus a projection of the storm's path. Four to eight inches of rain (yellow colors) is expected along the extreme northwest tip of Luzon Island. Image credit: NOAA Satellite Services Division.

Super Typhoon Melor hits Cat 5 strength
Super Typhoon Melor has become the second Category 5 tropical cyclone of the year. Melor is expected to recurve to the north pass just south of the coast of Japan later this week.

Jeff Masters

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moderate shear, with trouble ahead


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From 2006-
Member Since: June 28, 2006 Posts: 25 Comments: 8312
Good night folks from Mid-State TN. An interesting Tropical Weather week coming up!

TS Grace, the surprise TS will not live but 24-36 hrs.

TS Parma is gonna hang out in the S China Sea for 5 days, where's she gonna go?

Interesting to see if 91L develops and where she will go.

On Th 10-8-09, it will be very interesting to see how close TY Melor will get to Japan.

JTWC forecasts the center of TY Melor to pass within 25NMI of Japan's coast, as an 75KT TY near or just N of the Tokyo Metro area, which has an approx. population of 30,000,000 people on 10-8-09 shortly after 0800 UTC.
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Yellow through tomorrow Pm

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Quoting AussieStorm:
Rain storm on the way across Sydney
Link


Glad to see it's Raining somewhere in AU,
I have heard it's a Terrible Drought down there, AussieStorm. Hope you get some more rain soon. Those huge dust storms I hear about look to be awful. I have a good friend up in Darwin NT, and some long lost relatives in Melbourne. At least the Cyclones have been clear of AU this year, right? Good Luck to our Australian pals from us "Yanks". W in Florida.
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Yellow circle--waiting for a DMAX response--stabilization
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1030. xcool
ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT MON OCT 5 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON NEWLY-FORMED
TROPICAL STORM GRACE...LOCATED ABOUT 420 MILES NORTHEAST OF THE
AZORES.

1. A TROPICAL WAVE LOCATED ABOUT 1200 MILES EAST OF THE WINDWARD
ISLANDS IS PRODUCING A LARGE AREA OF DISORGANIZED SHOWERS AND
THUNDERSTORMS. SOME GRADUAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE
OVER THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD AT 15 TO 20 MPH.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS
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1029. 7544
Quoting btwntx08:

B.


orange
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1028. xcool
b
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Quoting WeatherStudent:
The 2am TWO from the NHC will have 91L inside of which colored circle:

A: Yellow Circle
B: Orange Circle
C: Red Circle

Please, vote now

Polls close in 15 minutes.


I think B, Orange Circle
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1022 Weather Student

2AM Yellow Circle
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1023. JLPR




im off to bed
night :0)
Member Since: September 4, 2007 Posts: 36 Comments: 5223
Quoting Bordonaro:


Thanks, believe or not, I understand that. If they allow systems like this to be considered TS, then the NHC/scientific textbook printing companies needs to consider changing SST threshold temperature. It's commonly taught that hurricanes need 80F SST to develop.


Yep, that paper on Hurricane Vince indeed suggests not using a SST threshold, but a lapse rate threshold.
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Quoting NCHurricane2009:


This is the way I interpreted the paper combined after hours of browsing the internet for other sources:

(1) Mature Extratropical Stage: At this stage, the surface extratropical cyclone features an occluded front, and has migrated beneath the center of an upper low (cold core).

(2) Subtropical cyclone stage: At this stage, the surface cyclone has separated from the occluded front and may feature a low-level warm core. If the upper-level low (cold core) allows for an unstable lapse rate, convection begins to develop, in some cases even over waters below 26 deg C. The convection triggers a more moist adiabatic lapse rate, which is even less stable. In the increasingly unstable atmosphere, air parcels increasingly rise, and low surface pressures are maintained or can fall.

(3) Tropical cyclone stage: At this stage, the convection has allowed for the development of a fully vertical warm core. The cyclone can continue to strengthen as long as it maintains deep convection, which allows for continued instability through super-moist adiabatic lapse rates.

The difference between stages (2) and (3) is how vertical deep the warm core is. The warm core is not involved in the strengthening process, just gives a signal of what stage its at. In both stages, the moist adiabatic lapse rate is dependent on the cyclone having a low central surface pressure such that it survives/strengthens.


Thanks, believe or not, I understand that. If they allow systems like this to be considered TS, then the NHC/scientific textbook printing companies needs to consider changing SST threshold temperature. It's commonly taught that hurricanes need 80F SST to develop.
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Quoting Bordonaro:


I am not a meteorologist, but I understand what you're explaining. Cool.

But the $64,000 question is this, "If an ULL mimics the set-up or dynamics of a hurricane, but develops in 70F water, shouldn't it be considered a Hybrid/Sub-Tropical System"?



This is the way I interpreted the paper combined after hours of browsing the internet for other sources:

(1) Mature Extratropical Stage: At this stage, the surface extratropical cyclone features an occluded front, and has migrated beneath the center of an upper low (cold core).

(2) Subtropical cyclone stage: At this stage, the surface cyclone has separated from the occluded front and may feature a low-level warm core. If the upper-level low (cold core) allows for an unstable lapse rate, convection begins to develop, in some cases even over waters below 26 deg C. The convection triggers a more moist adiabatic lapse rate, which is even less stable. In the increasingly unstable atmosphere, air parcels increasingly rise, and low surface pressures are maintained or can fall.

(3) Tropical cyclone stage: At this stage, the convection has allowed for the development of a fully vertical warm core. The cyclone can continue to strengthen as long as it maintains deep convection, which allows for continued instability through super-moist adiabatic lapse rates.

The difference between stages (2) and (3) is how vertical deep the warm core is. The warm core is not involved in the strengthening process, just gives a signal of what stage its at. In both stages, the moist adiabatic lapse rate is dependent on the cyclone having a low central surface pressure such that it survives/strengthens.
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JLPR---does look a little exaggerated--it has alot of work to do
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Goodnight all

Member Since: June 28, 2006 Posts: 25 Comments: 8312
Rain storm on the way across Sydney
Link
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Keeper, lives in Toronto Canada.
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1014. JLPR
Quoting GeoffreyWPB:
It does seem a bit overdone JL..this one has to have you a little bit worried.


yep a bit, but im relax until something actually actually forms :)
Member Since: September 4, 2007 Posts: 36 Comments: 5223
Been watching this blog for a while... lurking...

But Melor has been a beast...

NRl site has some good documentation of it; strangley holding on to Cat5/4 status well through its eye wall replacements.
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It does seem a bit overdone JL..this one has to have you a little bit worried.
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1011. JLPR
so ships sees a bright future for 91L taking it to H strength in 120hrs, TS in 24hrs
so TD soon?
it looks like a bit exaggerated, no? =P
Member Since: September 4, 2007 Posts: 36 Comments: 5223
Where do you live Keep?
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1009. KEEPEROFTHEGATE (Mod)
later all iam out catch around 7 am
Member Since: July 15, 2006 Posts: 170 Comments: 53602
1008. 7544
Quoting btwntx08:

holy wow



plus 1
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Quoting 7544:


this might help u

Link

thank you! it did help. have a good night all!
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Quoting homelesswanderer:


Would seem to gel with the graphic I posted.



Hi Homeless...
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Looking forward to Tim's forecast this morning.
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Quoting Orcasystems:


Nice place, I have been there many times :)


yea bloody cold right now though 42degrees here
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Last update for the night.. looking forward to watching the Zoo in the morning :)


AOI

AOI

AOI

AOI

Daily Chuckles in Comments section

Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting NCHurricane2009:


Here is a paper to support that theory (I think you can find this paper in Google)

Kwan-yin Kong. Understanding the Genesis of Hurricane Vince Through the Surface Pressure Tendency Equation . City College of New York.

This paper suggests a new paradigm in the thinking of how hurricanes form and develop.

Here is the current way we think: Deep bursts of convection over the center release latent heat, creating a strengthening vertical warm core over the center. A warmed column of air leads to low surface pressure (cyclonic spin at the surface) and high upper air pressure (upper anticyclone with cirrus outflow).

Here is the way this paper alters the thinking: Deep bursts of convection causes the central column of air to have a moist super-adiabatic lapse rate, thus resulting in a statically unstable atmosphere. The statically unstable atmosphere at the core of a hurricane causes air parcels to rise, causing low surface pressure and higher upper air pressure.

Now, this may explain why you can have a hurricane below 26 deg C water. All you need is to have a significantly unstable lapse rate to cause surface pressure falls. Over cooler sea surfaces, a cold core upper low over a deeply-occluded surface cyclone can allow for a super-unstable lapse rate due to the temp difference btn. the sea surface and cold core upper low.

I may have a post on this on my blog later this week (talk about skew-T diagrams, etc., so that this is understandable).


I am not a meteorologist, but I understand what you're explaining. Cool.

But the $64,000 question is this, "If an ULL mimics the set-up or dynamics of a hurricane, but develops in 70F water, shouldn't it be considered a Hybrid/Sub-Tropical System"?

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Quoting sarahjola:

is this something that has a good chance of happening? what strength might it be when it goes to florida, if it goes to florida?


That is a very long range model run. I would just watch Invest 91-L over the next few days.

I remember several days out earlier this season that (if I recall correctly) The Weather Channel showed a long range run of Hurricane Bill riding up the U.S. east coast, and then it ended up staying east of the U.S. east coast.
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Quoting Thopfner:
good evening Orca from Seattle myself


Nice place, I have been there many times :)
Member Since: October 1, 2007 Posts: 81 Comments: 26511
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA


THE BERMUDA HIGH BUILDING WESTWARD ACROSS THE NORTHERN GULF OF
MEXICO WILL QUICKLY WASH OUT THE STALLED FRONT BY TUESDAY.

FURTHER-UP...HIGH PRESSURE BUILDING NORTHEAST OUT OF CENTRAL OLD
MEXICO TO ACROSS LOUISIANA...WILL SHUT DOWN THE PACIFIC WESTERLY
WAVE TRAIN. A DRIER MIDTROPOSPHERE IS EXPECTED

MONDAY NIGHT...SIGNIFICANT ADVECTIVE WARMING AND MOISTENING WILL
TAKE PLACE...AS LONG-FETCH SOUTHERLIES CARRY NORTHWEST-CARIBBEAN AIR
INTO THE WESTERN UPPER GULF COAST STATES. THE OVERNIGHT MINIMUMS
WILL BE RUNNING ABOUT 10 DEGREES ABOVE NORMAL.


FOR TUESDAY...THE WARM-UP AND MOISTENING-UP CONTINUES. THE AFTERNOON
MAXIMUMS WILL BE RUNNING ABOUT 10 DEGREES ABOVE NORMAL...WHILE THE
AFTERNOON HUMIDITIES WILL BE RUNNING ABOVE NORMAL.


They better not stall my cold front! I'll have to talk to Ike about this in the morning! ;-)
Lol. Good night all.
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good evening Orca from Seattle myself
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995. 7544
Quoting sarahjola:

is this something that has a good chance of happening? what strength might it be when it goes to florida, if it goes to florida?


this might help u

Link
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994. 7544
yeap 91L has alotof moisture to work with and could really put on a show at dmax tonight . looks like it will all be with the timming of the front on where 91L could wind up wait and watch for now but dmax could be interesting tonight
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I just noted that there were some posts over the past couple of days about Danny and Erika shouldn't have been named.

Just curious, wondering why some are thinking they were not tropical cyclones? I though they were just sheared tropical cyclones.
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Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting NCHurricane2009:



From running that animation, I saw Invest 91-L going into the western Caribbean, then getting recurved northeastward into the Gulf of Mexico, taking a trip across Florida, and then deepening into a strong nor'easter after becoming extratropical.

is this something that has a good chance of happening? what strength might it be when it goes to florida, if it goes to florida?
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Quoting sarahjola:

i am a weather idiot. lol! where is that graphic saying its going to go. is it going to the gulf? be gentle please!



From running that animation, I saw Invest 91-L going into the western Caribbean, then getting recurved northeastward into the Gulf of Mexico, taking a trip across Florida, and then deepening into a strong nor'easter after becoming extratropical.
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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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