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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Quoting blsealevel:
I think this is what Reedzone was looking at eirler, I know I saw it, dosn't weaker storms tend to not be affected by Northerly Trough's as stronger ones do? but it still modeled to go NW this will change and start the widow washer effect soon though i think anyway.
That's why he was saying he thought this would get closer to the US coast than models are portraying before it's all over. Just so long as it doesn't get far enough west to negatively impact the Bahamas I'm ok...
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Quoting AussieStorm:
Is that a CoC on 92L?



I saw that too, but I see the center more west than your mark. But, spin in animation looks weak like this is still an open wave, but a sharp one at that.
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2009. JavPR
where can i see the models that develop that central atl wave?
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2008. Relix
Our CATL wave is destined to be a fish storm it seems.
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Quoting weatherman12345:
quick question:
since the nhc already found winds of 60 mph would that be the intesnsity when they find a LLC.


40-50 mph TS.
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I think this is what Reedzone was looking at eirler, I know I saw it, dosn't weaker storms tend to not be affected by Northerly Trough's as stronger ones do? but it still modeled to go NW this will change and start the widow washer effect soon though i think anyway.
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Keeper, are you talking left turn or dissipation? I think either are possible...but it does seem he is drifting more north than west at this hour, but slowly

Quoting KEEPEROFTHEGATE:
be funny if colin ends up pulling a fast one and exits stage left
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1997. KEEPEROFTHEGATE 10:36 PM EDT on August 04, 2010
be funny if colin ends up pulling a fast one and exits stage left



Would not be funny at all if it comes over my head in the process....
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Quoting hurricanejunky:


Nice forecast on Xtreme Weather! You are a talented young dude!


LOL, I have a more downcasted view of 92L and Colin.
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Quoting hurricanejunky:


Nice forecast on Xtreme Weather! You are a talented young dude!
Thank you.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
1997. KEEPEROFTHEGATE (Mod)
be funny if colin ends up pulling a fast one and exits stage left
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Is that a CoC on 92L?

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That is possible. I am just saying what weather12345 and others are saying...he could miss the trough, or he could center relocate, or he could begin moving north.

Quoting heretolearninPR:


I thought that slowing could also mean the beginning of a change in direction. Is it time for ex-Colin to be heading North?
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1994. BDAwx
Night all! Be safe.
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I notice that Invests coming off the Mexican coast become Depressions very quick. Best looking Storm this season was in the Pacific. With all the hype about this Atlantic season it has to start soon.
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Quoting angiest:


Looks like the position of the center, within a few tens of miles, may have a major impact on where he goes.


Looking at CIMMS 850, realizing the weak state of the LLC and shear in place, Colin is a prime candidate for a center relocation.

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For the SE coast it now really looks like Colin will no longer be an issue. Even though it is building again there is a good area of drier air and high wind shear that it would need to move through.

Link

Link
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1988. 7544
Quoting KEEPEROFTHEGATE:
04L/XX/XX
MARK
19.93N/62.56W


hes expoding and not moving
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Just this side of heaven is a place called Rainbow Bridge.

When an animal dies that has been especially close to someone here, that pet goes to Rainbow Bridge.
There are meadows and hills for all of our special friends so they can run and play together.
There is plenty of food, water and sunshine, and our friends are warm and comfortable.

All the animals who had been ill and old are restored to health and vigor; those who were hurt or maimed are made whole and strong again, just as we remember them in our dreams of days and times gone by.
The animals are happy and content, except for one small thing; they each miss someone very special to them, who had to be left behind.

They all run and play together, but the day comes when one suddenly stops and looks into the distance. His bright eyes are intent; His eager body quivers. Suddenly he begins to run from the group, flying over the green grass, his legs carrying him faster and faster.

You have been spotted, and when you and your special friend finally meet, you cling together in joyous reunion, never to be parted again. The happy kisses rain upon your face; your hands again caress the beloved head, and you look once more into the trusting eyes of your pet, so long gone from your life but never absent from your heart.

Then you cross Rainbow Bridge together....

Author unknown...
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Evening,

Colin's storm activity looks even more organized this afternoon. But, I don't think its as organized as it might seem. The remnant surface trough of Colin is analyzed to be north of the Lesser Antilles, which puts the lowest surface pressures west of the nicely organized circular storm bursts. Unless surface pressures are falling beneath the circular bursts for a new surface low pressure center to form there, Colin is struggling from the ULL (upper level low0 to its west and may not come back.
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1985. KEEPEROFTHEGATE (Mod)
he waiting for something
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Quoting MiamiHurricanes09:
Blog Update!

August 4, 2010 - 9:15 PM EDT - Tropics Getting Active


Nice forecast on Xtreme Weather! You are a talented young dude!
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Quoting Goldenblack:
Sorry to repeat myself, Colin is slowing = one step to bad news. If he slows he presents more of a threat....





I have to respectfully disagree. Colin slowing down means that it is no longer being influenced by the ridge and Low level jet and is approaching the weakness shown by the models. Should start accelerating to the northwest in the next 12-24 hours
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1981. KEEPEROFTHEGATE (Mod)
04L/XX/XX
MARK
19.93N/62.56W
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Quoting earthlydragonfly:
evening night shift!
Evening Earthly
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1979. angiest
Quoting CyclonicVoyage:
Explains the NW drift out of Colin right now.



Looks like the position of the center, within a few tens of miles, may have a major impact on where he goes.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1970.

The other thing: once on the west side of that ULL (if that ever actually happens) the ULL has a different effect, more of an enhancement if Colin gets going. I'm more interested in seeing if Colin can hold it together overnight. After that we should get some HH data into the models and that will give a better idea of what's really going on up there...
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evening night shift!
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Explains the NW drift out of Colin right now.

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Quoting Goldenblack:
Sorry to repeat myself, Colin is slowing = one step to bad news. If he slows he presents more of a threat....




I thought that slowing could also mean the beginning of a change in direction. Is it time for ex-Colin to be heading North?
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1973. 7544
if he keeops hanging out and drifting west hes gonna miss that trof
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Sorry to repeat myself, Colin is slowing = one step to bad news. If he slows he presents more of a threat....


Quoting 7544:
colins drifting west at this hour hmmmmmm
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1969. KEEPEROFTHEGATE (Mod)
Quoting leo305:
what a monstrous amount of convection in the Central Atlantic
all the better to make storms with
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aqua, those are cool snaps. That 'coon looks like he's been invited.... lol would u believe they are invasive here? Somebody brought a couple in as pets and they "escaped" into the bush. We had problems with them eating our mangos all summer....
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Should see 93L tomorrow out in the CATL
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Be back in a bit to check on the 11 pm update - daughter is calling now...
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1965. 7544
colins drifting west at this hour hmmmmmm
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1964. tkeith
Quoting angiest:


Dunnol about crocs, but gators are good eatin'. :)
I have a whole book of nuthin but Gator recipes...I like fried tail the best, and gator sausage is a close second :)
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The Atlantic is alive and well you downcasters!!! (nothin but love)

Quoting leo305:
what a monstrous amount of convection in the Central Atlantic
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1962. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15620

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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.