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 Seflhurricane:
too much windshear maybe friday what i want to see is the models on the new center


An anti-cyclone has developed over the system, so wind shear is actually on the way down. However, the anticyclone could fall apart and allow Colin to be sheared again. Hard to say. Like I said, trends need to continue. They won't re-designate Colin until the hunters investigate.
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Quoting Hurricanes101:
941. SeniorPoppy 9:28 PM GMT on August 04, 2010

I agree too, but of course the person you commented towards also decided to put everyone down by basically saying that they are wishcasting if they don't think this will affect Bermuda. It makes it hard to even talk about the tropics when everything many say on here is considered a wishcast by a few


Well like you said, who is wish-casting this to go west? Nobody today that I've seen. :)
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Trans-casters :D
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Quoting Drakoen:


Yea. Right now it looks like 50% as to whether it is back or not.


Agreed. Maybe at 11 we might see a regenerated Colin but not yet.
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941. SeniorPoppy 9:28 PM GMT on August 04, 2010

I agree too, but of course the person you commented towards also decided to put everyone down by basically saying that they are wishcasting if they don't think this will affect Bermuda. It makes it hard to even talk about the tropics when everything many say on here is considered a wishcast by a few
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Quoting extreme236:
Recon is going back in at 00z to determine if it has a closed circulation. Then we can determine if we have Colin again or not.
arent they scheduled for 8Pm tonight ???
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Quoting extreme236:
Recon is going back in at 00z to determine if it has a closed circulation. Then we can determine if we have Colin again or not.


Yea. Right now it looks like 50% as to whether it is back or not.
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Looks like i called it (If Colin is a TC according to the navy) but i was just 4 to 5 hours late.
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Quoting MississippiWx:
Colin has the classic appearance of a developing tropical storm. I could easily see him being a hurricane this time tomorrow, if this trend continues.
too much windshear maybe friday what i want to see is the models on the new center
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Recon is going back in at 00z to determine if it has a closed circulation. Then we can determine if we have Colin again or not.
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Quoting MississippiWx:
I think the NHC will re-designate Colin as a tropical storm at the 11pm advisory after the hurricane hunters have investigated the system. Of course, that's all assuming Colin keeps up the trend.
maybe sooner thay can issue a special statement/advisory at any time i am thinking at around 8pm or before 11pm
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948. 7544
Quoting sammywammybamy:
Guys i think their gonna Upgrade Collin.

It went from 04L REM LOW to 04L Collin


thats what i thought looks like its a td now and will show on the next
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Colin has the classic appearance of a developing tropical storm. I could easily see him being a hurricane this time tomorrow, if this trend continues.
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Quoting sammywammybamy:
Guys i think their gonna Upgrade Collin.

It went from 04L REM LOW to 04L Collin


Not on the ATCF site. It still says WV. So no TS Colin yet.
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looks like colin is back
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Colin looks good but it all depends on the circulation
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click to enlarge.



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Quoting Hurricanes101:
not sure what the 1 was either

I find it rather insulting that people keep on saying that some are wishcasting or laying out unrealistic scenarios when I have yet to see one person say this would hit the US

again I guess it is just someone who likes to bust chops or just wants to see what kind of crap they can cause on the blog, because I have not seen anyone say anything about Ex-Colin impacting the US


1 means agree. Mainly to due with Bermuda being possibly in the line of fire.
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If Colin regenerates it will be TS Colin not TD Colin btw.
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Quoting 7544:


thanks

navy doesent show remant low now it shows o4l colin does this mean its a td again as of the navy site
not sure but ya its shows 04L COLIN

2010 Storms
All Active Year


Atlantic
92L.INVEST
04L.COLIN

East Pacific
99E.INVEST
97E.INVEST

Central Pacific

West Pacific
97W.INVEST
96W.INVEST

Indian Ocean
90B.INVEST

Southern Hemisphere
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Quoting StormW:


Hard to say what the NHC will do...with the requirements they have.


And depending on how whoever the forecaster on duty interprets those rules...
Member Since: August 26, 2006 Posts: 16 Comments: 4766
I think the NHC will re-designate Colin as a tropical storm at the 11pm advisory after the hurricane hunters have investigated the system. Of course, that's all assuming Colin keeps up the trend.
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not sure what the +1 was either

I find it rather insulting that people keep on saying that some are wishcasting or laying out unrealistic scenarios when I have yet to see one person say this would hit the US

again I guess it is just someone who likes to bust chops or just wants to see what kind of crap they can cause on the blog, because I have not seen anyone say anything about Ex-Colin impacting the US
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Quoting weatherman12345:
POLL TIME!
8:00PM TWO EX.COLIN
A.20%
B.30%
C.40%
D.50%
E. STRAIGHT TO RED


E
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AOI

AOI

AOI

AOI

AOI

TS BUSTED FORECAST ALIBI
Member Since: October 1, 2007 Posts: 81 Comments: 26511
932. 7544
d
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Quoting StormW:


Hard to say what the NHC will do...with the requirements they have.
but in terms of how ex colin looks does it appear like its regenerating , looks that way to me but i like to hear from the expert like you
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Quoting weatherman12345:
POLL TIME!
8:00PM TWO EX.COLIN
A.20
B.30
C.40
D.50
E. STRAIGHT TO RED


B or C
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E
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928. 7544
Quoting Seflhurricane:
more west but slight north component


thanks

navy doesent show remant low now it shows o4l colin does this mean its a td again as of the navy site
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Quoting weatherman12345:
POLL TIME!
8:00PM TWO EX.COLIN
A.20
B.30
C.40
D.50
E. STRAIGHT TO RED


D.
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Quoting weatherman12345:
POLL TIME!
8:00PM TWO EX.COLIN
A.20
B.30
C.40
D.50
E. STRAIGHT TO RED
E
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Quoting cg2916:


What's the whole +1 thing about?


Bermuda should remain vigilant with regards to ex-Colin.
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NMFC Norfolk Tropical Feed
NO Active Tropical Warnings in the Atlantic, Caribbean, or Gulf of Mexico
By Maritime.CDO@navy.mil (NMFC CDO) from Naval Maritime Forecast Center Norfolk Virginia. Published on .

As of Wed 04 Aug 2010 21:15:01Z
2010 Storms
All Active Year

Atlantic
92L.INVEST
04L.COLIN
East Pacific
97E.INVEST
99E.INVEST
Central Pacific
NONE
West Pacific
97W.INVEST
96W.INVEST
Indian Ocean
90B.INVEST
Southern Hemisphere
NONE
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Quoting SeniorPoppy:


+1


What's the whole +1 thing about?
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Quoting SeniorPoppy:


It will be Karen...LOL

LMAO!!! funny!
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Quoting 7544:
is he moving n or wnw
more west but slight north component
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convection with 92L may have decreased some, but environmental conditions are very favorable, and it will be passing over very high heat content in the next 24 hours.
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916. 7544
is he moving n or wnw
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Quoting SeniorPoppy:


It will be Karen...LOL


LOL
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Quoting xCat6Hurricane:
funny how everyone trys to find out every possible scenario for something, the unthinkable.

The bottom-line is Colin will be going for a swim out to sea, keep Bermuda in your prayers.


+1
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does anyone check out stormpulse.com?

I ask only because they have 92L's location at 12.8N 76.6W while the WU site has it at 14.0N 73.9W... as of 2pm EDT

and that's kind of a big difference...
comments?
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Quoting Tazmanian:



it would be 11pm


Sometimes they name it in-between advisories.
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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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