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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GFS 18z 96 hours, Danielle off to the fishes but Earl lurking in the eastern Atlantic. Note the 1011mb low with a closed isobar in the EATL.

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1111. Drakoen
Quoting Levi32:


Yeah the 2nd one that's trying to form but I think that because of the other one to the west, it's not fully closed at the surface. The one northeast of Puerto Rico looks closed but should cease to be the anchoring circulation eventually.


You may be right though the northerlies extend out towards the British virgin islands.
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Quoting all4hurricanes:
Do you think Colin is siphoning convection from 92/8L?



Yeah! If I look real close, I think I see the hose!!
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I say its closed off around 19.5N/63W, the new COC/LLC for TS colin soon to be again imo.
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Quoting SLU:


True. I still think if there was enough evidence of the closed low that they would reclassify the system.
more than likely before calling it they will wait for recon to confirm
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1107. SLU
Quoting Seflhurricane:
the NHC has also been very conservative thus far this season


True. I still think if there was enough evidence of the closed low that they would reclassify the system.
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nic wave

Member Since: May 21, 2006 Posts: 5091 Comments: 114653
1105. Levi32
Quoting psuweathernewbie:
Levi32, the 2nd one is the one to the northeast of Puerto Rico, the first one is the dying one north of Puerto Rico.


That's what I said.
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How many times is that image gonna be posted of Colin? I mean, it looks nice, but it's not superficial! :)
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Levi32, the 2nd one is the one to the northeast of Puerto Rico, the first one is the dying one north of Puerto Rico.
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Quoting HurricaneSwirl:


It showed that in a run yesterday or so and showed a strong TS go into east TX.


Is that SE Texas?
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Do you think Colin is siphoning convection from 92/8L?
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Colin's remnants continue to produce more organized convection as time goes on, this could get bad. Although he has slowed down considerably, he does not look like an immediate threat to the US East Coast, exception probably being Bermuda.
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Quoting SLU:
Lots of persistent observations showing south to southwest winds over the islands which means that the circulation is getting better defined but it doesn't necessarily mean that it is fully closed. If it was then the NHC would have responded accordingly. We need to get a ship report or a buoy or any kind of observation closer to the center of northwest to west winds to confirm a fully closed low. Right now it looks pretty much semi-closed more than anything. We are going to lose the benefit of visible imagery soon which would leave us in the dark tonight .. so to speak.

the NHC has also been very conservative thus far this season
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GFS 18z 78 hours, Danielle is off to the fishes.

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Quoting HurricaneSwirl:


It's not, it comes from the tail end of a front.



ok
Member Since: May 21, 2006 Posts: 5091 Comments: 114653
Quoting CybrTeddy:


No, it develops off a trough split.



oh
Member Since: May 21, 2006 Posts: 5091 Comments: 114653
Quoting Tazmanian:



i think thats 92L


It's not, it comes from the tail end of a front.
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1093. Drakoen
GFS showing a decent storm that while curving out to sea it appears to be holding its own.
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1092. xcool


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1091. Levi32
Quoting Drakoen:


I would place the center of Colin on the western edge of the convection based on the surface observations.


Yeah the 2nd one that's trying to form but I think that because of the other one to the west, it's not fully closed at the surface. The one northeast of Puerto Rico looks closed but should cease to be the anchoring circulation eventually.
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Quoting Drakoen:


I would place the center of Colin on the western edge of the convection based on the surface observations.
looks right
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Quoting Tazmanian:



i think thats 92L


No, it develops off a trough split.
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Quoting CybrTeddy:
12z ECMWF also shows a low in the Gulf at 144 hours.


It showed that in a run yesterday or so and showed a strong TS go into east TX.
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Quoting CybrTeddy:
12z ECMWF also shows a low in the Gulf at 144 hours.



i think thats 92L
Member Since: May 21, 2006 Posts: 5091 Comments: 114653
Quoting KEEPEROFTHEGATE:
LATEST AS OF 555 PM EDT



It's alive!!!!..It's alive!!!!! followed by.. evil laughter
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1085. SLU
Lots of persistent observations showing south to southwest winds over the islands which means that the circulation is getting better defined but it doesn't necessarily mean that it is fully closed. If it was then the NHC would have responded accordingly. We need to get a ship report or a buoy or any kind of observation closer to the center of northwest to west winds to confirm a fully closed low. Right now it looks pretty much semi-closed more than anything. We are going to lose the benefit of visible imagery soon which would leave us in the dark tonight .. so to speak.

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Quoting CybrTeddy:


Yup, 12z ECMWF 48 hours out.


Here it comes gang, we're going to see storm after storm after storm.
looks like we are going to have the explosion thats being predicted , hope it all stays away from the USA and especially Florida
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Quoting CybrTeddy:
12z ECMWF also shows a low in the Gulf at 144 hours.


It also weakens Danielle.
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Quoting Levi32:


Yeah it's closed northeast of Puerto Rico with the mid-level circulation off to the east of it with the convection. It's a tropical storm in reality, just a disorganized one.
No I'm seeing a closed low based on those surface observations just to the west of that new convective blow up north of the U.S/British Virgin Islands.
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1081. 7544
Quoting CybrTeddy:


Yup, 12z ECMWF 48 hours out.


Here it comes gang, we're going to see storm after storm after storm.


but will they all go fishing ?
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1080. Drakoen
Quoting Levi32:


Yeah it's closed northeast of Puerto Rico with the mid-level circulation off to the east of it with the convection. It's a tropical storm in reality, just a disorganized one.


I would place the center of Colin on the western edge of the convection based on the surface observations.
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12z ECMWF also shows a low in the Gulf at 144 hours.
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Colin looks good, but is in a bad place.
East Atlantic looks bad, but is in a good place imho.
Member Since: July 11, 2006 Posts: 14 Comments: 11143
Winds at St. Croix have become WNW in the past hour. Hmmmmm......
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Quoting stormpetrol:

You are right I think that is actually the LLC remnants of Colin, I think the ball of convection was the around only area the HH flew today,I don't think they investigated 20N/65W, I could be absolutely 100% wrong, I think the area round 19.5/61.5W is the MLC that is working its way down to the surface and become the dominant one, the other is basically the old LLC swirl of Colin, jmo.


I think it is a surface low trying to close off.
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Quoting MiamiHurricanes09:
GFS 18z 48 hours, both the Euro and the GFS are in agreement that we will have Danielle in 48 hours.



48 hours? Had no idea it was that soon lol. If that's the case the disturbance around the CV islands should get a 20% chance in the next TWO.. well that's what I would do.
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Quoting Snowlover123:


Hopefully that one will be an East Coast storm, since 04L looks to be a fish storm... :(
Ummm...ok? Fishes are good.
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Quoting Drakoen:
With both the ECMWF and GFS showing development in the eastern Atlantic within 48 hours, the NHC needs to mention the disturbance SW of the CV islands.


Yup, 12z ECMWF 48 hours out.


Here it comes gang, we're going to see storm after storm after storm.
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Quoting 7544:
from the remains to a low back to a ts the nhc took off all the plots they must be scratching their head
not really colin just literraly collapsed and is coming back i have seen this happen often
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1069. Levi32
Quoting Drakoen:
It would be difficult for me to believe there is not a closed circulation now associated with Colin based on these surface observations:



Yeah it's closed northeast of Puerto Rico with the mid-level circulation off to the east of it with the convection. It's a tropical storm in reality, just a disorganized one.
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1068. KEEPEROFTHEGATE (Mod)
LATEST AS OF 555 PM EDT

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Quoting Snowlover123:


Hopefully that one will be an East Coast storm, since 04L looks to be a fish storm... :(


Uhh why?
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ex colin is also over the herbert box just as an FYI
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1064. 7544
from the remains to a low back to a ts the nhc took off all the plots they must be scratching their head
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Quoting MiamiHurricanes09:
GFS 18z 48 hours, both the Euro and the GFS are in agreement that we will have Danielle in 48 hours.




wish storm lol
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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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