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 divdog:
98l tag was a mistake it was for a system that went into mexico a couple of weeks ago


98L went into mexico and 99L formed over Mexico
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Quoting largeeyes:
Ha! I wasn't crazy!

" This storm was being tagged as 98L yesterday; I'm not sure why it is being called 92L today."
98l tag was a mistake it was for a system that went into mexico a couple of weeks ago
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sammy, so there was a quick drop in pressure before that gust...interesting.
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Thanks as always for the very informative update, Dr. Masters, but you did make one error; you wrote:

The CSU team did decrease their Accumulated Cyclone Energy (ACE) forecast slightly, from 185% of average to 178% of average.

...but that's not entirely correct. The CSU team still calls for a total seasonal ACE of 185%; the 178% is what was left after July 31st, as there was already 7% before that date.
Member Since: November 8, 2009 Posts: 4 Comments: 13529
Quoting PRweathercenter:

I agree, it could go south, or north, only time will tell


It could do donuts in the open Atlantic..
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Satellite imagery suggests that 92L continues to get better organized developing deeper and more organized convection. 92L is also accompanied by an anticyclone in the upper levels providing favorable conditions wind shear-wise along with better outflow. Total Precipitable Water also suggests that 92L is associated with some broad cyclonic curvature, satellite imagery depicts the same story. I'm keeping the chance of 92L developing into a tropical cyclone in the next 48 hours at moderate (30-50%).
Member Since: September 2, 2009 Posts: 130 Comments: 21193
well guys we all know it only takes 10 reports to get rid of it
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Quoting AllStar17:
It's too early to tell where the African tropical wave will go.

I agree, it could go south, or north, only time will tell
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When is the NOAA outlook scheduled to come out?
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Quoting cg2916:
Do I smell ANOTHER JFV?


Unfortunately, yes.
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Ha! I wasn't crazy!

" This storm was being tagged as 98L yesterday; I'm not sure why it is being called 92L today."
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Quoting Floodman:


Just keep your shower curtain handy...you'll be fine
Just put up a new shower curtain. Been looking for a fish one but no luck. Made do with generic el-cheep o from Dollar General but I don't think it's got the MoJo.
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It's too early to tell where the African tropical wave will go.
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Quoting hydrus:
I believe they will re-evaluate hurricane Alex, and it will be listed as a major hurricane. But I will keep the crow pot ready..:)


Ya the pressure was low enough, but winds never caught up and I think all the ingredients have to be there for them to re-classify.
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wow sammywammybamy have you ever bothered to look at the pressures they are pritty darn high

I mean look at it

Station 41044
NDBC
Location: 21.652N 58.695W
Conditions as of:
Wed, 4 Aug 2010 14:50:00 UTC

Winds: SE (140°) at 31.1 kt gusting to 38.9 kt
Significant Wave Height: 10.2 ft
Dominant Wave Period: 8 sec
Atmospheric Pressure: 30.07 in and rising
Air Temperature: 75.6 F
Dew Point: 73.8 F
Water Temperature: 83.5 F

30.07in=1018.2 and rising

but I have to say nice work on catching out the winds and wave hight


oh yes also new surface maps are out and it seems that ex-RL colin in now a surface trough and a tropical wave

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Quoting Relix:
T-Wave off Africa should follow Colin's path

yeah, it should, however check all this high pressures forming north, it could go south of the greater antilles, only time will tell
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Quoting Floodman:


Just keep your shower curtain handy...you'll be fine


Ha!
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Quoting Floodman:


Just keep your shower curtain handy...you'll be fine



he'll never live down that shower curtain.
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When does NOAA issue their forecast?
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Quoting Relix:
T-Wave off Africa should follow Colin's path


relix = susan soltero
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Quoting AllStar17:
I am tracking three areas of interest, all of which have a shot at (re)development:

1. Remnants of Colin
2. Invest 92L
3. African Wave

I'm closey watching number 3
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Quoting Floodman:


Just keep your shower curtain handy...you'll be fine
Nuthin can penetrate the omnipotent all powerful curtain......Good mornin Flood.
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Blog update! Hope you guys find it informative.
Ex-Colin and 92L need to be watched
Member Since: July 8, 2005 Posts: 259 Comments: 24018
Quoting Orcasystems:


Oh sure.. take the conservative track like the NHC... right down the centre :)



LOL...yep
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T-Wave off Africa should follow Colin's path
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Quoting weathermanwannabe:
Being it is early August and we have a few "spins" out there (including Colin) with gradually improving overall conditions as we head towards mid-August, I think it's only a matter of time (Aug to Sept) when we will see some "clusters" out there with two or three storms going at one time IMHO.


If 2008 can do four, we can sure as heck do five.
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Here's the relevant page from Dr. Gray's updated seasonal forecast:

Member Since: November 8, 2009 Posts: 4 Comments: 13529
Quoting 2010StormNames:
StormW, and to think that we have yet to even see our first major of the year, let alone the actual 5 that CSU is expecting to form. We've still got a longs wayyyyyyyyyyyy to go. Potential very dangerous times lies ahead of all of us, right, Storm?
I believe they will re-evaluate hurricane Alex, and it will be listed as a major hurricane. But I will keep the crow pot ready..:)
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Quoting sammywammybamy:
Station 41044
NDBC
Location: 21.652N 58.695W
Conditions as of:
Wed, 4 Aug 2010 14:50:00 UTC

Winds: SE (140°) at 31.1 kt gusting to 38.9 kt
Significant Wave Height: 10.2 ft
Dominant Wave Period: 8 sec
Atmospheric Pressure: 30.07 in and rising
Air Temperature: 75.6 F
Dew Point: 73.8 F
Water Temperature: 83.5 F





Whoa. Someone.. LOOK AT THIS!
Most common last words of a Red Neck: "Hey y'all, look at me!"

2nd most common: "Git me a stick and I'll poke it."
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Hi everyone,
I think we should see a significant increase in activity next week as the MJO gets more in the positive phase in the Atlantic. I think we are now just in the neutral phase?
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Being it is early August and we have a few "spins" out there (including ex-Colin) with gradually improving overall conditions as we head towards mid-August, I think it's only a matter of time (Aug to Sept) when we will see some "clusters" out there with two or three storms going at one time IMHO.
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Quoting wunderkidcayman:
so what Orca this is going to be 93L then hmmm lol


I don't make predictions... a forecaster I am not. I look at AOI's that I think look like they will become something, and then track them.

Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting 2010StormNames:
StormW, and to think that we have yet to even see our first major of the year, let alone the actual 5 that CSU is expecting to form. We've still got a longs wayyyyyyyyyyyy to go. Potential very dangerous times lies ahead of all of us, right, Storm?


Just keep your shower curtain handy...you'll be fine
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Blobwatchers
Quoting Orcasystems:


I prefer to be considered Robustly Petite :)
Sounds better then a beach ball with fingers


rofl
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so what Orca this is going to be 93L then hmmm lol
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Quoting sammywammybamy:

This is the most recent image. An increase in convection:

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Quoting Kristina40:
So storm should refer to Orca as "Big Mammal".


I prefer to be considered Robustly Petite :)
Sounds better then a beach ball with fingers
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting KEEPEROFTHEGATE:
thanks doc

i bet a lot are surprized by no change in numbers


i reckon wanting to stick to your guns...
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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.