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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Will be interesting if the next invest is 99L or 93L, considering we skipped over 99-90-91
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I wanna see aquak9! :)
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803. Upload them to ur wonderphotos, aqua, then link. I would like 2 see them.
Member Since: October 25, 2005 Posts: 19 Comments: 22322
805. jasoncoolman2010xx 8:52 PM GMT on August 04, 2010

He didnt say we had 93L, he said we could have 93L out of the area by 30W
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Quoting Sfloridacat5:


Going on 7 straight days of thunderstorms at our house (Fort Myers area). The field by the neighborhood is completely underwater.
Dog's having a nervous breakdown from all the thunder.




He's away from the keyboard,but tell the Dogs I completely understand.
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Quoting Drakoen:
Colin center fix:

looks like we may have RED on the next TWO
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Quoting Seflhurricane:
thanks drak now i am seeing what appears to me a new center forming with ex colin, i pinpointed near 61.8W and 19.5N your thoughts


That looks right
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totally off-topic, but with all the heat, I've got a raccoon that keeps visiting for water and food. I have pics, but don't wanna get flagged.

Anyone wanna see the raccoon?
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802. xcool


Member Since: September 26, 2009 Posts: 2 Comments: 15684
overall the remnants of colin looks like a sheared tropical storm to me and is beginning to look much better and has pretty good outflow to the east side
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Colin center fix:

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I wasn't sure becuase I used the NHC satellite imagery for the lat/lon, but the blowup just began with ex-colin's new center. This looks the most intimidating now for Colin, then at anytime during his lifespan.
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i think we will see 93 and 94L this week
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Quoting Hurricanes101:


center looks closer to 61W to me right by the blowup of convection
yes i just zoomed in and it looks like its trying to close off but still poorly defined , still looking at the vorticy maps and info to confirm
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796. xcool
;;;
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting Drakoen:


Looks like we have a similar set-up to what produced Colin. A circulation is developing west of 30W above 10N in the ITCZ. A pouch from a tropical wave is located northeast of this circulation and as the pouch moves westward it will begin to interact with the ITCZ disturbance to possibly form a tropical cyclone. The reliable computer forecast models forecast for development in this region.
thanks drak now i am seeing what appears to me a new center forming with ex colin, i pinpointed near 61.8W and 19.5N your thoughts
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Quoting Hurricanes101:


center looks closer to 61W to me right by the blowup of convection
Yup, that center that they are tracking is the old center of Colin.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Patrap:





Going on 7 straight days of thunderstorms at our house (Fort Myers area). The field by the neighborhood is completely underwater.
Dog's having a nervous breakdown from all the thunder.

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Quoting Seflhurricane:
i would say more like 62.7W but close enough and yes i believe a new center is forming there !!! and you can see the old center north of puerto rico


center looks closer to 61W to me right by the blowup of convection
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still think Ex colin will be too weak to be picked up by the trough and the models are going by the old center not the new one trying to develop so i would not go too much with the models right now
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Quoting MiamiHurricanes09:
ACE (Accumulated Cyclone Energy) So Far

1. Alex - 6.78
2. Colin - 0.358
3. Bonnie - 0.245
-----------------------------
Total: 7.383

I would've sworn Alex's ACE was higher. Oh well...
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788. xcool
Tazmanian .yea ;)
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting Seflhurricane:
hey drak what are your thoughts on the wave SW of the Cape Verde Islands


Looks like we have a similar set-up to what produced Colin. A circulation is developing west of 30W above 10N in the ITCZ. A pouch from a tropical wave is located northeast of this circulation and as the pouch moves westward it will begin to interact with the ITCZ disturbance to possibly form a tropical cyclone. The reliable computer forecast models forecast for development in this region.
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786. xcool
scott39 .not much
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting xcool:



may be 93L
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Quoting MiamiHurricanes09:
ACE (Accumulated Cyclone Energy) So Far

1. Alex - 6.78
2. Colin - 0.358
3. Bonnie - 0.245
-----------------------------
Total: 7.383


Colin, a TS for 6-12 hours, beats out Bonnie? Wow.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting psuweathernewbie:
Colin's new center is around 63W and 19.8N. Does anyone disagree? Would it still be Colin given that his old center is moving quickly westward north of Puerto Rico? Also the upper level low to his NNW looks to be moving more quikcly to the north then Colin is moving?
i would say more like 62.7W but close enough and yes i believe a new center is forming there !!! and you can see the old center north of puerto rico
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Quoting Drakoen:
92L gaining some spin:

Not bad.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting sky1989:


Lol! There are some indications that it may but with the MJO continuosly changing and upward motion coming into the Atlantic, along with the NAO possibly going negative, the pattern can change. Of course, the wave in the Carribean (92L)could beat it to becoming Danielle.



plugging ears lalala lalala lalala...lol
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Quoting Hurricanes101:


that is the poorly defined center that has up to this point been preventing Colin from closing off by the convection. The fact that it is becoming ill-defined increases the chances that Colin will be able to get his own circulation better organized


That sounds OK. :) Unfortunately it is either too far away from the radar or there isn't much convection right there to look at, because the reflections are very weak.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Only problem with Colin strengthening later is that the GFS doesn't seem to initialize the 2nd center near Puerto Rico on the 850mb maps. With the GFS low resolution it's hard to say but it could give Colin more trouble if it can't concentrate the center in one spot, but we'll see.
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Quoting Drakoen:
92L gaining some spin:

hey drak what are your thoughts on the wave SW of the Cape Verde Islands
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Quoting xcool:
scott39 i think so
Wonder how far W it will go now?
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Colin's new center is around 63W and 19.8N. Does anyone disagree? Would it still be Colin given that his old center is moving quickly westward north of Puerto Rico? Also the upper level low to his NNW looks to be moving more quikcly to the north then Colin is moving?
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ACE (Accumulated Cyclone Energy) So Far

1. Alex - 6.78
2. Colin - 0.358
3. Bonnie - 0.245
-----------------------------
Total: 7.383
Member Since: September 2, 2009 Posts: 130 Comments: 21194
AS THE REMNANTS OF COLIN CONTINUE NORTHWARD TOMORROW...EXPECT A
SHIFT IN SYNOPTIC WIND FLOW TO A MORE SOUTHERLY
DIRECTION...STEERING ADDITIONAL TROPICAL MOISTURE ACROSS THE LOCAL
ISLANDS. FORECAST FOR PW REFLECTS THIS TREND...PEAKING OUT NEAR
2.5 INCHES ACROSS THE LOCAL ISLANDS ON SATURDAY MORNING. AT THIS
TIME...BEST CHANCE FOR PRECIP APPEARS TO BE LATE FRIDAY OR
SATURDAY AS THIS MOISTURE STREAMS ACROSS THE LOCAL ISLANDS...WITH
A RELATIVELY "DRY" SLOW AHEAD OF THE PEAK...COMBINED WITH THE
INTENSIFICATION OF THE SUBEQUATORIAL RIDGE OVER THE LOCAL
ISLANDS...HELPING TO LIMIT SHOWER DEVELOPMENT SOMEWHAT TOMORROW.
NO SIGNIFICANT WEATHER FEATURES TO SPEAK OF IN EXTENDED FORECAST
AT THIS TIME


..hmm no significant weather features... what about all that convection near africa i would say thats significant
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769. xcool
scott39 i think so
Member Since: September 26, 2009 Posts: 2 Comments: 15684
as for Ex colin the next TWO might say satellite images and surface observations indicate that the remnates of colin are becoming better organized.
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Quoting ho77yw00d:


I can live with that my name can just move on out to sea lol


Lol! There are some indications that it may but with the MJO continuosly changing and upward motion coming into the Atlantic, along with the NAO possibly going negative, the pattern can change. Of course, the wave in the Carribean (92L)could beat it to becoming Danielle.
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Quoting Jeff9641:


Danielle is going to be a bad u know!




SHHHHHHHHHHHH dont say that JEFF
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92L gaining some spin:

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Quoting ho77yw00d:
GEETING NAILED IN FORT MYERS/SANIBEL AREA...AGAIIIIN....!!!!



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Quoting xcool:


Looks like W right now.
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Quoting MiamiHurricanes09:
looks good Miami lets see if the NHC will mention it on the next TWO Does it have any model support
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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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