CSU leaves their hurricane forecast unchanged; 92L and Colin's remains worth watching

By: Dr. Jeff Masters , 2:38 PM GMT on August 04, 2010

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Tropical Storm Colin was ripped apart by wind shear yesterday, and the storm's remnants are passing just north of the northernmost Lesser Antilles Islands today. Most of the heaviest thunderstorms are passing north of the islands, as seen on Guadeloupe radar. Long range radar out of Puerto Rico also shows this. Colin's remains are in a rather unfavorable environment for re-development, since the disturbance is passing beneath an upper-level low pressure system with dry air and high wind shear. Wind shear is a high 20 - 25 knots over Colin's remains this morning. Recent satellite imagery shows that heavy thunderstorm activity has increased in intensity and areal coverage over the past few hours, though, and Colin's remnants will need to be monitored for re-development.

Forecast for Colin's remains
The latest SHIPS model forecast predicts that wind shear will drop from 15 - 25 knots today to a moderate 15 - 20 knots on Thursday. Wind shear will continue to decline over the weekend, and this relaxation of shear prompts most of the major models to predict re-development of Colin sometime in the next four days. NHC is giving Colin's remain a 20% chance of developing into a tropical depression by Friday morning. A major trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough will pull Colin to the northwest and cause it to slow down. By Friday, Colin will be moving at half of its current speed. All of the major forecast models are predicting that the trough of low pressure will be strong enough to fully recurve Colin out to sea early next week. Colin's remains may pass close to Bermuda on Saturday, with the latest 06Z (2am EDT) run of the GFDL model predicting that Bermuda will experience tropical storm force winds on Saturday as Colin passes to the west of the island. The Hurricane Hunters are scheduled to investigate Colin's remains at 8pm EDT tonight. It currently appears that Colin will only be a threat to Bermuda and Canada.


Figure 1. Morning satellite image of Colin's remains and Invest 92L.

92L
A tropical wave (Invest 92) in the south-central Caribbean is moving west at 15 - 20 mph. This wave is over warm water and is experiencing low wind shear of 5 - 10 knots, and could show some development over the next two days. However, the wave's rapid westward motion should bring it ashore over Nicaragua and Honduras on Friday, or the Yucatan Peninsula on Saturday, and 92L probably does not have enough time over water to develop into a tropical depression. NHC is giving a 20% chance of this disturbance developing into a tropical depression by Friday morning. This storm was being tagged as 98L yesterday; I'm not sure why it is being called 92L today.

CSU's forecast numbers for the coming hurricane season remain unchanged
A very active Atlantic hurricane season is on tap for 2010, according to the seasonal hurricane forecast issued today, August 4, by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team continues to call for 18 named storms, 10 hurricanes, 5 intense hurricanes, and an Accumulated Cyclone Energy (ACE) index 185% of average. These are the same numbers as their June 2 forecast. 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 14 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast continues to call for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (50% chance, 31% chance is average) and the Gulf Coast (49% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also high, at 64% (42% is average.)

The forecasters cited four main reasons for an active season:

1) Moderate La Niña conditions should be present during the most active portion of this year's hurricane season (August - October). This should lead to reduced levels of vertical wind shear compared with what was witnessed in 2009.

2) Current SST anomalies are running at near-record warm levels. These very warm waters are associated with dynamic and thermodynamic factors that are very conducive for an active Atlantic hurricane season.

3) Very low sea level pressures prevailed during June and July over the tropical Atlantic. Weaker high pressure typically results in weaker trade winds that are commonly associated with more active hurricane seasons.

4) We are in the midst of a multi-decadal era of major hurricane activity, which began in 1995. Major hurricanes cause 80 - 85 percent of normalized hurricane damage.

Analogue years
The CSU team picked four previous years when atmospheric and oceanic conditions were similar to what we are seeing this summer. Those four years were 2005, the worst hurricane season of all time; 1998, which featured 3 major hurricanes, including Category 5 Hurricane Mitch; 1952, a relatively average year that featured just 7 named storms, but 3 major hurricanes; and 1958, a severe season with 5 major hurricanes. The mean activity for these five years was 17 named storms, 11 hurricanes, and 5 intense hurricanes, almost the same as the 2010 CSU forecast.

How accurate are the August forecasts?
The August forecasts by the CSU team over the past 12 years have had a skill 21% - 44% higher than a "no-skill" climatology forecast for number of named storms, hurricanes, intense hurricanes, and the ACE index (Figure 2). This is a good amount of skill for a seasonal forecast, and these August forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. This year's August forecast uses a new formula, so we don't have any history on how the technique has behaved in the past. An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.61 to 0.65 for their previous August forecasts using different techniques, which is respectable.


Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August), using the Mean Squared Error. The British firm Tropical Storm Risk (TSR) will issue their outlook for the 2010 Atlantic hurricane season on June 4. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

The British private forecasting firm Tropical Storm Risk, Inc. (TSR) is scheduled to release their August forecast later today. NOAA will also be issuing their August forecast sometime in the next week.

This season has had three named storms so far (Alex, Bonnie, and Colin.) It will be difficult to have a season with 19 or more named storms, since the four seasons that had at least 19 named storms all had at least five named storms by this point (August 4.) These four seasons were 1887, 1933, 1995, and 2005.

Next update
I'll have an update on Thursday morning.

Jeff Masters

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2712. breald
Quoting Jeff9641:


Basically they said they expect an explosion in storms to occur over the next 2 weeks and one member from the NHC was on TWC last night and he said he really feels the US coast especially the SE US is for a big one or two down the road. Very ominious tone while listening to there discussions last night.


But it seems like it takes a month for a storm to form. We were tracking ex-Colin for weeks before it was decleared a TD.
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Drakoen, what is your take on the Central Atlantic area?
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2708. Engine2
Quoting reedzone:


The steering maps clearly show it moving NW, then a bit WNW, then north, and then it recurves. Based on those maps, I haven't seen any other front then the one expected to recurve it.

yet again Reed I agree with you
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Quoting BahaHurican:
Did u see the OPC map for Monday that I posted? I think the models are assuming the newer front will move swiftly enough to push Colin very east very fast. I don't know how that gels with the stationary low over FL, but...


The steering maps clearly show it moving NW, then a bit WNW, then north, and then it recurves. Based on those maps, I haven't seen any other front then the one expected to recurve it.
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Storm,

Pete and Repete were on a boat. Pete fell off. Who was left?
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At what point(if any) will Colin make hurricane status, and what's the chance of us here on the east coast (NC) picking up any groundswell from him? I'm thinking it will be minimal at most, due to his rapid forward motion and recurve, he'll be out of our 'window'. Unless we can pick up some backswell....
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2703. Drakoen
NASA GOES Animation reveals that Ex-Colin has a well-defined circulation.
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2702. help4u
yes,if not longer.
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Oh and good morning!
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Quoting CyclonicVoyage:


Seems to be a different map than what I am looking at??

Oh because I use the CIMSS PREDICT site. I don't think that there is a difference except the site I use updates every hour.
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2698. IKE
2690...I don't think weather456 would have to create a new handle. I haven't seen eye to eye with him on everything but he's never done anything to require a new handle.

Why do I get the feeling you are from south Florida?
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I'm sure most of you have seen videos like this before, but whether you have or have not, they're pretty fascinating. This one is a time lapse of the entire 2008 North Atlantic hurricane season. Viewing it, you'll notice how difficult it is even in a busy season for things to form; there's a lot more that goes into building a storm than just an ample supply of hot water. You'll also notice that, while we're focused on tropical phenomenon here, TCs are actually a fairly small part of a very large picture.

Member Since: November 8, 2009 Posts: 4 Comments: 13568
Quoting reedzone:
According to the steering maps, Colin should recurve right in the middle of the East Coast and Bermuda. The BAMMS is showing this while the other models take it too far east.
Did u see the OPC map for Monday that I posted? I think the models are assuming the newer front will move swiftly enough to push Colin very east very fast. I don't know how that gels with the stationary low over FL, but...
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so steering patters will predominately be recurves for CV storms for the next few weeks huh?
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Quoting MiamiHurricanes09:
Ex-Colin still holding out to the 40mph winds, however the pressure has decreased by 1mb to 1008mb. Interestingly enough it remains as a "wave".

AL, 04, 2010080512, , BEST, 0, 230N, 650W, 35, 1008, WV,

Watching Colin is almost like listening to "the Boxer" by S&G.
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2692. help4u
You get a line and i get a pole baby and will go down to the fishin hole!lol
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Quoting pensacolastorm:


Where does this image come from?



Here
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Quoting sammywammybamy:


Heyyy. Long Time No See!


Hey Sammy.......where you been hinding sorta like me as well...i avoid the blog mostly but, just pop in on occasions.
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Quoting MiamiHurricanes09:
Really? I see plenty of 850mb vorticity up near 12N 31W.



Seems to be a different map than what I am looking at??

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Quoting ShenValleyFlyFish:
Reported


ROFLMAO, what did you spike your morning coffee with :)
Member Since: October 1, 2007 Posts: 81 Comments: 26511
2686. Drakoen
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Quoting TampaSpin:
Looks like Colin might become a Hurricane but, fishin he goes.


Member Since: October 1, 2007 Posts: 81 Comments: 26511
COC exposed.
Member Since: July 8, 2005 Posts: 259 Comments: 24190
According to the steering maps, Colin should recurve right in the middle of the East Coast and Bermuda. The BAMMS is showing this while the other models take it too far east.
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I really don't like this negative NAO that StormW was talking about either especially living on the West side of Florida. Anything that comes up out of the Caribbean will have a chance to recurve into Florida's West Coast. The setup is very simialar to what you would find in late October or November.



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2679. Drakoen
Morning visible images sugggest that Ex-Colin that, while Ex-Colin is asymmetric, the system is developing a well-defined circulation near 23.4N 65.1W.
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2678. IKE
Exposed center at 23.5N and 65.2W?...speed it up all the way....
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2677. help4u
Active season but with the strong smell of fish!
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2676. barbamz
"Fish" - Rov vid saved from the GOM Sea bottom some minutes ago http://de.tinypic.com/r/c442b/4
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Quoting obxnagshead:
If Colin gets its act together is there a chance it will head more northwest or is it for sure going to go to the north and totally miss the east coast? Thoughts...


Fish
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Looks like Colin might become a Hurricane but, fishin he goes.
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Quoting obxnagshead:
If Colin gets its act together is there a chance it will head more northwest or is it for sure going to go to the north and totally miss the east coast? Thoughts...
I'm not quite seeing that Bermuda strike just yet, but if things play out more or less as forecast it seems unlikely OBX will see any of Colin...
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Quoting extreme236:
GFS more than recurves the CATL wave, it pretty much sends it NW and then to the N shortly after development. Keeps it well away from the Caribbean islands.
Let's hope that verifies...
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I am truly amazed how the Bermuda High weakens so much this time of year for such a long period of time before making a comeback. We better hope nothing develops into the Caribbean during that time.
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Quoting Jax82:


Miami, even since the NHC hasnt even mentioned it in their discussion or drawn a yellow circle around it?
Well yeah, we probably will need some recognition in the TWO, but as soon as there is we are likely to see 93L.
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Hey, is anybody else seeing the TUTT as repositioned along a line approximately 30N/65W 26N/74W 22N/90W? If what I'm seeing on the WV loop is correct, looks like the TUTT may be shifting, which would give the next few storms to approach the Antilles a better chance of formation....
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2666. IKE
Quoting breald:
Morning. NOAA will come out with their new predictions today at 11am. Do you think they will lower their numbers?


I'm surprised the others didn't...just slightly.

To answer your question...either no or just slightly.
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2664. Jax82
Quoting MiamiHurricanes09:
When recon goes to investigate ex-Colin later today I think we'll have a TS again. I also think that we'll see 93L out of the large and vigorous tropical wave in the CATL in the next 48 hours.


Miami, even since the NHC hasnt even mentioned it in their discussion or drawn a yellow circle around it?
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If Colin gets its act together is there a chance it will head more northwest or is it for sure going to go to the north and totally miss the east coast? Thoughts...
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Ex-Colin still holding out to the 40mph winds, however the pressure has decreased by 1mb to 1008mb. Interestingly enough it remains as a "wave".

AL, 04, 2010080512, , BEST, 0, 230N, 650W, 35, 1008, WV,
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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.