CSU and TSR continue to predict a near-average hurricane season

By: Dr. Jeff Masters , 3:18 PM GMT on August 04, 2009

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A tropical disturbance embedded in the Intertropical Convergence Zone (ITCZ), near 9N 35W, is moving west at about 15 mph. The heavy thunderstorm activity associated with this tropical wave has changed little over the past 24 hours, and remains disorganized. This morning's QuikSCAT pass showed a moderate wind shift, but nothing resembling an organized surface circulation. Top winds were in the 20 - 30 mph range. Strong easterly winds are creating about 20 knots of wind shear over the wave, which is marginally conducive for development. The disturbance is about 300 miles south of the Saharan Air Layer (SAL), so dust and dry air should not hinder development over the next few days.

Given the disturbance's current lack of organization, combined with the presence of 20 knots of wind shear, any development should be slow to occur. The forecast wind shear along the storm's path over the next five days is predicted to remain at or below 20 knots, which should allow some slow development. Sea surface temperatures (SSTs) will warm from about 28°C to 29°C as the storm progresses westward. The GFS model has been indicating some development is possible in several of its runs over the past few days, but has not been consistent with this prediction. None of the other models show any development of the system. NHC is giving the disturbance a low (less than 30% chance) of developing into a tropical depression over the next two days, which is a good forecast. The GFS and ECMWF models predict the system will be approaching the northern Lesser Antilles Islands by Sunday. Both models forecast the development of a band of very high wind shear just to the north of the islands at that time, so the long-range survival of anything that might manage to develop is in doubt.

CSU forecast team continues to predict an average hurricane season
A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued August 4 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 10 named storms, 4 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 83% of average. Between 1950 - 2000, the average season had 10 named storms, 6 hurricanes, and 2 intense hurricanes. But since 1995, the beginning of an active hurricane period in the Atlantic, we've averaged 15 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is a step down from their June forecast, which called for 11 named storms, 5 hurricanes, and 2 intense hurricanes. Their April forecast called for 12 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast calls for a near-average chance of a major hurricane hitting the U.S., both along the East Coast (27% chance, 31% chance is average) and the Gulf Coast (26% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane (37%; 42% is average).

The forecasters noted that while sea surface temperature anomalies have increased in the tropical Atlantic and surface pressures have fallen in recent weeks, which normally would favor higher hurricane activity, the presence of El Niño conditions in the Eastern Pacific should counteract these influences. They forecast that the current weak El Niño event will strengthen to a moderate event by September:

El Niño events tend to be associated with increased levels of vertical wind shear and decreased levels of Atlantic hurricane activity. Tropical Atlantic sea surface temperatures anomalies have warmed somewhat since our early June prediction and surface pressures have fallen somewhat. But, the negative influences of El Niño-induced strong Caribbean Basin and Main Development Region vertical wind shear typically dominate over surface pressure and sea surface temperature in the tropical Atlantic.



Figure 1. Change in Sea Surface Temperature anomaly (in °C) between July 2009 and May 2009. Most of the tropical Atlantic has warmed, relative to normal, over the past 2 months. Image credit: NOAA/ESRL.

Analogue years
The CSU team picked four previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: weak to moderate El Niño conditions, and average tropical Atlantic and far northern Atlantic SSTs. Those four years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 1965, which had Category 3 Betsy that hit New Orleans; 1963, which had Category 4 Hurricane Flora that devastated Cuba; and 1957, which didn't have any hurricanes that hit hit land during the peak part of hurricane season. The mean activity for these four years was 9 named storms, 4 hurricanes, and 2 intense hurricanes--almost the same as the 2009 CSU forecast.

How accurate are the August forecasts?
The August forecasts by the CSU team have historically offered a skill of 45 -62% higher than a "no-skill" forecast using climatology (Figure 2). However, they are using a new forecast scheme this year, so it is difficult to judge how skillful this year's forecast might be.


Figure 2. Accuracy of long-range forecasts of Atlantic hurricane season activity performed at Colorado State University (CSU) by Dr. Bill Gray's team (colored squares) and Tropical Storm Risk, Inc. (TSR, colored lines). The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

August 2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) also issued a new forecast today, and have increased their numbers by 20% from their June and July forecasts. TSR is also calling for a near-average season, predicting 12.6 named storms, 6.5 hurricanes, 2.8 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 103% of average. Their June forecast called for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are slightly above the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TSR predicts a 40% chance of an above-average season, 44% chance of a near-average season, and a 19% chance of a below-average season, as defined by ACE index. TSR rates their skill level as 51% above chance at forecasting the number of named storms, 60% skill for hurricanes, and 44% skill for intense hurricanes. These are far higher skill numbers than the June ones: 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.8 named storms will hit the U.S., with 1.6 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these August forecasts for U.S. landfalls is 25% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.1 named storms, 0.5 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites one main factor for their increased forecast: higher sea surface temperatures than expected over the tropical Atlantic, due to the fact that the trade winds over the Atlantic should be slower than originally anticipated. Faster than average trade winds create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling.

The CSU and TSR groups are done making forecasts for the coming hurricane season, but NOAA is still due to put out an August update.

I'll have an update on Wednesday.
Jeff Masters

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Quoting TampaFLUSA:

Rm34667 was mistaken, he was referring to a different disturbance..Dr M said Dean WOULD form.

Okay, I'm not supposed to be messing around in this now anyway as I'm in critical meltdown with my projects. Will check back later!
Member Since: July 11, 2006 Posts: 14 Comments: 11410
Quoting Chicklit:

This is the same crew whose Chief Met says "no land affected" by Felicia and her brother Enrique. How is HI looking? Do you think the Island chain will be spared?


Cutting it close.
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Quoting BurnedAfterPosting:


shows you how quickly things can change
and vice versa
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Quoting IKE:
Steve Lyons...Tropical update..."fair weather out in the Atlantic."

This is the same crew whose Chief Met says "no land affected" by Felicia and her brother Enrique. How is HI looking? Do you think the Island chain will be spared?
Member Since: July 11, 2006 Posts: 14 Comments: 11410
Quoting Chicklit:
Interesting RM 34667...SSTs are warmer now than then. Shear is also the variable for this unnamed entity since SAL isn't really a problem, particularly if it stays low.
Hey Petrol! Good instincts. Let us know when you begin to smell it. Imagine we'll get more insight then! LOL.

Rm34667 was mistaken, he was referring to a different disturbance..Dr M said Dean WOULD form.
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My post in 751 was not accurrate. I have modified it. I think the first paragraph was in reference to a different area. It it still interesting to go back and read. There is also an image of dean at that time.
Member Since: September 7, 2006 Posts: 5 Comments: 912
Quoting HaboobsRsweet:

only good in the short term...long term it hurts because people go into debt and buy things they cant afford so after the storm passes the economy is way down plus takes awhile for some of those businesses to reopen or for the people to return after they evac.
That is true, but you are missing the beginning of this "conversation" from Mobilegirl...of which statements make no sense whatsoever. There are laws to combat price gauging. If oil is affected, than so may be gas prices. If insurance claims rise, so may insurance. But to say they will not discuss potential development in order to curtail economic increases is ridiculous.
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Hurricane Felicia

Statement as of 2:00 PM PDT on August 04, 2009

satellite images indicate that Felicia has developed a ragged eye
and a symmetrical outflow pattern. Dvorak intensity estimates at
1800 UTC supported an intensity of 65 kt but since that time... the
eye has become better-defined on satellite images. Thus the initial
intensity is raised to 70 kt...making Felicia the third hurricane
of the 2009 eastern Pacific season.
The hurricane has been in a rapid intensification phase today...and
with environmental conditions forecast to be conducive for further
strengthening...the question is: how strong will it get? The
presence of an eye on both the 85 and 37 ghz channels of a 1547 UTC
ssmis microwave pass supports more strengthening...even a
continuation of rapid intensification. The SHIPS rapid
intensification index also forecasts a 62 percent chance of a 30-kt
increase in strength within 24 hours...about 8 times the Sample
mean. Although the dynamical models are less aggressive...
the
official NHC forecast will lean on SHIPS and the microwave data to
forecast rapid intensification during the next 24 hours and level
off the winds thereafter as the cyclone moves over progressively
cooler waters. In the longer-term...increasing westerly shear may
also help to weaken the Hurricane.




Felicia continues moving toward the west...280/12. A ridge to the
north of the hurricane is expected to slowly erode due to a large
upper-level trough near 130w. This should allow Felicia to move
more to the west-northwest by tomorrow. In a couple of days...there
is the potential for Enrique to cause further ridge weakening...
which could allow for a slower and slightly more poleward motion of
Felicia. There is considerable divergence in the model guidance
with the GFDL/HWRF/ECMWF showing more interaction between the two
tropical cyclones and the UKMET/NOGAPS showing virtually none. For
now...i'm going to lean on the guidance that shows more separation
between the two cyclones and the official forecast lies just south
of the model consensus.

Forecast positions and Max winds

initial 04/2100z 12.4n 126.6w 70 kt
12hr VT 05/0600z 13.0n 128.3w 85 kt
24hr VT 05/1800z 13.9n 130.1w 95 kt
36hr VT 06/0600z 14.7n 131.7w 100 kt
48hr VT 06/1800z 15.5n 133.3w 100 kt
72hr VT 07/1800z 16.5n 137.0w 90 kt
96hr VT 08/1800z 17.5n 142.5w 80 kt
120hr VT 09/1800z 17.5n 148.5w 65 kt

$$
forecaster Blake
Member Since: July 3, 2005 Posts: 427 Comments: 129439
763. IKE
Steve Lyons...Tropical update..."fair weather out in the Atlantic."
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Interesting RM 34667...SSTs are warmer now than then. Shear is also the variable for this unnamed entity since SAL isn't really a problem, particularly if it stays low.
Hey Petrol! Good instincts. Let us know when you begin to smell it. Imagine we'll get more insight then! LOL.
Member Since: July 11, 2006 Posts: 14 Comments: 11410
761. IKE
Quoting BurnedAfterPosting:


shows you how quickly things can change


Dr. Masters wasn't referring to pre-Dean/90L there...that's another blob.
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760. Skyepony (Mod)
Cloudsat pass from this morning of the Atl Blob.



You can see where the rain blends with the water surface. Very heavy rain.

Also from slumming today's cloudsat I've gathered the NE quadrent of Morakot is way more moist than the SW side.
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Storm Relative 16km Geostationary Water Vapor Imagery 2100 UTC

Member Since: July 3, 2005 Posts: 427 Comments: 129439


last sat images, show a little more organized
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670. archer312

Will be heading your way, to Pantherville, Saturday. What kind of weather should we expect?

From Charleston - Where the Ashley River meets the Cooper River to form the Atlantic Ocean.
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Quoting RMM34667:
Wow I looked through the Blog Archieves. Here is August 12. One Day before Dean is becomes an invest.

Posted by: JeffMasters, 2:02 PM GMT on August 12, 2007

Thunderstorm activity in association with a surface trough of low pressure over the Western Caribbean remains disorganized. None of the computer models than reliably forecast tropical storm formation are calling for development in this region. Wind shear is about 20 knots, which will keep any development slow.


He was right...Dean did not form in the western Carib...Dr M said the following about the EASTERN Atl 90l
1) A strong trough of low pressure is forecast to move off the East Coast of the U.S. at that time, and this trough may deflect 90L northwards so that it misses the Lesser Antilles Islands, and then recurves harmlessly out to sea.

2) In keeping with the steering pattern we've observed since late July, the trough is expected to rapidly move onward, allowing a ridge of high pressure to build in. If the trough is not strong enough to recurve 90L out to sea, the storm will be forced to the west once more and eventually hit the East Coast of the U.S. This is the solution of last night's ECMWF model.

3) 90L will be far enough south and next weekend's trough will be weak enough that 90L will plow through the Caribbean, and not be deflected north of the Lesser Antilles Islands. The storm would eventually track into the Gulf of Mexico. This is the solution preferred by this morning's GFS model.

4) 90L will never develop, or will never become more than a weak tropical storm, due to unfavorable wind shear, dry air, or other factors. This is the solution of the NOGAPS model.

Of the four scenarios, I believe #2 or #3 are most likely to occur--90L will develop into a tropical storm or hurricane that will affect the Caribbean and/or U.S. East Coast. Residents throughout the Caribbean and U.S. should anticipate the possibility that 90L may become a hurricane--and possibly a major hurricane--that will not recurve. If you plan on being in the Lesser Antilles Islands Thursday August 16 - Sunday August 19, keep in mind there is a heightened risk of a tropical storm or hurricane during that period. Be prepared to adjust your travel plans.

So I dont get what your saying.
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Quoting AllStar17:
Weather456, StormW (if on):

Thoughts on our AOI. New convection firing where 850 mb vort maximum is. Do you think that will become the main player, or should we still watch the MLC farther to the west?


My opinion: I think we should watch the MLC because it is heading into a more favorable environment.....the 850 mb vort max. is moving more NW and into a less favorable environment...the MLC is vice versa (more favorable environment)
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Multiplatform Tropical Cyclone Kinetic Energy and Intensity,Hurricane Felicia

Member Since: July 3, 2005 Posts: 427 Comments: 129439
Multiplatform Satellite Surface Wind Analysis
Hurricane Felicia 1800 UTC

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751. RMM34667
10:49 PM GMT on August 04, 2009
Wow I looked through the Blog Archieves. Here is August 12. One Day before Dean is becomes an invest.

Posted by: JeffMasters, 2:02 PM GMT on August 12, 2007

Sorry. correcting for accurracy. After reading the blog again I blieve his opening paragraph was in reference to another area. again Sorry.

Link
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750. AllStar17
10:49 PM GMT on August 04, 2009
Quoting weatherwatcher12:
Favorable shear forecast


Not good news.
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749. weatherwatcher12
10:47 PM GMT on August 04, 2009
Favorable shear forecast
Member Since: May 16, 2009 Posts: 1 Comments: 1231
748. Patrap
10:47 PM GMT on August 04, 2009
RAAMB Currently Active Tropical Cyclones


* Current Active Cyclones


Last Updated 11 Minutes Ago


Hurricane Felicia Visible Image

Member Since: July 3, 2005 Posts: 427 Comments: 129439
747. tmangray
10:47 PM GMT on August 04, 2009
Watching the mutual proximity of Enrique and Felicia for any signs of a Fujiwhara Effect. Felicia has rapidly intensified today and appears to have a bead on the big island of Hawaii.
746. AllStar17
10:46 PM GMT on August 04, 2009
Weather456, StormW (if on):

Thoughts on our AOI. New convection firing where 850 mb vort maximum is. Do you think that will become the main player, or should we still watch the MLC farther to the west?
Member Since: June 29, 2009 Posts: 13 Comments: 5315
744. gator23
10:43 PM GMT on August 04, 2009
Quoting SafeInTexas:


No, using credit cards are buying more debt and interest payments, instead of paying off debt. A massive overload of debt is what is causing a lot of our current problems. Search up the broken windows fallacy.

The bakers window was dirty scratched and full of bird poo. He needed anew window anyway. Having a new window will make his pies clearer to see and more appetizing to consumers therefore he doubles his sales.

J/K
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743. AllStar17
10:42 PM GMT on August 04, 2009
Felicia looking impressive

Member Since: June 29, 2009 Posts: 13 Comments: 5315
742. Chicklit
10:41 PM GMT on August 04, 2009
Dean per Wikipedia:
Link
Reference "nuttin' gettin' into Caribbean"
ShearMap
As of this map it's 30 knots with 40 knots inside of that.
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741. AllStar17
10:41 PM GMT on August 04, 2009
What will Dr. Lyons say this hour?
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739. JLPR
10:39 PM GMT on August 04, 2009
This is getting confusing =S
now we apparently have a low at 30W but the wave behind it apparently wants to join the party too
and the mid level low is running off to the west so I guess if everything combines it could mean

LLC + Mid-level circulation + tropical wave = Ana?

xD
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738. SafeInTexas
10:38 PM GMT on August 04, 2009
Quoting atmoaggie:

I don't get it. Everyone spends money with an impending landfall. Even Gustav-like cat2s with a fairly small windfield cause mass buying on the credit cards. Wouldn't that be great for the economy?


No, using credit cards are buying more debt and interest payments, instead of paying off debt. A massive overload of debt is what is causing a lot of our current problems. Search up the broken windows fallacy.
Member Since: September 19, 2005 Posts: 0 Comments: 64
737. gator23
10:38 PM GMT on August 04, 2009
Quoting Chicklit:
Last time I checked there were 40 if not 50 knots of shear in the Caribbean. I cannot imagine how anything's going to get in there.
She's locked up tighter than a King's daughter in spring.

when was the last time you checked?
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736. atmoaggie
10:38 PM GMT on August 04, 2009
Quoting HaboobsRsweet:

only good in the short term...long term it hurts because people go into debt and buy things they cant afford so after the storm passes the economy is way down plus takes awhile for some of those businesses to reopen or for the people to return after they evac.

I hear ya about the long term issues. However, if I locally drop a couple of thousand that would have otherwise been sent to my debtors or saved...
Member Since: August 16, 2007 Posts: 6 Comments: 12463
735. victoria780
10:38 PM GMT on August 04, 2009
Quoting IKE:


Just about unwatchable. I watch local on the 8's and not much more unless the Atlantic has something.

Miss hearing John Hope.
The people they have for the Tropical Update are pitiful,other then a few meteorologists they are not worth watching..
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734. BurnedAfterPosting
10:37 PM GMT on August 04, 2009
Every forecast model I have seen decreases shear in the Caribbean in the next 4-5 days
733. gator23
10:37 PM GMT on August 04, 2009
Quoting Chicklit:
Last time I checked there were 40 if not 50 knots of shear in the Caribbean. I cannot imagine how anything's going to get in there.
She's locked up tighter than a King's daughter in spring.

uh...
Member Since: August 26, 2008 Posts: 0 Comments: 2182
732. Chicklit
10:37 PM GMT on August 04, 2009
Last time I checked there were 40 if not 50 knots of shear in the Caribbean. I cannot imagine how anything's going to get in there.
She's locked up tighter than a King's daughter in spring.
Member Since: July 11, 2006 Posts: 14 Comments: 11410
731. stormpetrol
10:35 PM GMT on August 04, 2009
Quoting Chicklit:

Care to elaborate Petrol? I'm outta time for looking stuff up. Have to be finishing projects and traveling for two days! Crapola.
I will miss all the fun in here.

If I remember correctly Pre Dean was under easterly shear much like this disturbed area and had a similar appearance from what I remember, I could be dead wrong though.
Member Since: April 29, 2007 Posts: 0 Comments: 8134
730. gator23
10:35 PM GMT on August 04, 2009
Quoting atmoaggie:

I don't get it. Everyone spends money with an impending landfall. Even Gustav-like cat2s with a fairly small windfield cause mass buying on the credit cards. Wouldn't that be great for the economy?

i dont buy on credit my supplies are paid for at the start of the season. If your prepared credit shouldnt matter.
Member Since: August 26, 2008 Posts: 0 Comments: 2182
729. java162
10:34 PM GMT on August 04, 2009
Quoting stormpetrol:
For some reason this area of disturbed weather around 9-11N/30-36W reminds me of the birth of Hurricane Dean 2007.


i hope it doesn't turn out to be like dean. i'm from the island of dominica in the lesser antilities and hurricane dean( although it passed about 60 miles to our south) caused alot of public infrastructural damage...
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728. Chicklit
10:33 PM GMT on August 04, 2009
Quoting stormpetrol:
For some reason this area of disturbed weather around 9-11N/30-36W reminds me of the birth of Hurricane Dean 2007.

Care to elaborate Petrol? I'm outta time for looking stuff up. Have to be finishing projects and traveling for two days! Crapola.
I will miss all the fun in here.
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727. Stormchaser2007
10:33 PM GMT on August 04, 2009
Disorganized at the moment

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726. HaboobsRsweet
10:32 PM GMT on August 04, 2009
Quoting atmoaggie:

I don't get it. Everyone spends money with an impending landfall. Even Gustav-like cat2s with a fairly small windfield cause mass buying on the credit cards. Wouldn't that be great for the economy?

only good in the short term...long term it hurts because people go into debt and buy things they cant afford so after the storm passes the economy is way down plus takes awhile for some of those businesses to reopen or for the people to return after they evac.
Member Since: May 20, 2009 Posts: 0 Comments: 1640
725. Chicklit
10:32 PM GMT on August 04, 2009
Quoting Dropsonde:
I am fascinated by the two areas of interest around our disturbance. We have the area of high low-level vorticity at 10N30W and the area of high upper-level vorticity ("the" blob) at 9N36W. It may be the result of the easterly shearing that has taken place today, but I'm not sure that 20-25kts could account for such a distance between the two areas of circulation. I am more inclined to think it is an artifact of how the original African wave came off the coast, with the robust (then) mid-level circulation trailing and coming off farther north than the main convective area.

If you look back at the old runs of the GFS, this is exactly what it predicted for this time today. It furthermore predicts that the 10N 30W blob, the one that is gaining convection right now, will become dominant, pulling the blob we've been watching all day into it, and THAT is what will develop.

It's an interesting scenario, and it seems like it would make for a potent system, between the low-level vorticity of the 30W system and the vast moisture envelope of the 36W one. Development farther north than expected also would give the system an edge in lifting out of the ITCZ.

I think a lot hinges on how well the two areas do this evening. If either of them develops, it basically has to pull in the energy of the other one. This evening we will probably get a good idea as to which one will win.

Thank-you, Dropsonde, for that analysis sans ego or prejudice. Simple observation.
How refreshing!
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724. stormpetrol
10:29 PM GMT on August 04, 2009
For some reason this area of disturbed weather around 9-11N/30-36W reminds me of the birth of Hurricane Dean 2007.
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723. Patrap
10:28 PM GMT on August 04, 2009
As Ive stated before,..when novices come here and spread Falsehoods of that type,..it only hurts the good folks who devote their lives to the Science of Tropical Forecasting.

Folks jump in here on the wu,make outlandish statements with no basis in fact,well thats schoolyard recess banter at best.

And if you want,you can ask the folks at the NHC those questions personally as they have a easy to find web address.



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722. atmoaggie
10:27 PM GMT on August 04, 2009
Quoting gator23:

why katrina

I don't get it. Everyone spends money with an impending landfall. Even Gustav-like cat2s with a fairly small windfield cause mass buying on the credit cards. Wouldn't that be great for the economy?
Member Since: August 16, 2007 Posts: 6 Comments: 12463

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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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