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 Levi32:


It just means that the CFS thinks this will be the most powerful La Nina ever recorded, but it likely won't get that strong.
I would like to see the affects it has on the Atlantic basin.
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Quoting TexasHurricane:


what does that mean?



That means its going to be a VERY STRONG La Nina
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Quoting Levi32:
Holy snap....Some of the latest CFS member forecasts (blue lines) now predicting a La Nina of below -3.0!



Hmm...very reminiscent of 1998.

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Quoting Levi32:


It just means that the CFS thinks this will be the most powerful La Nina ever recorded, but it likely won't get that strong.



CA could be in for a vary cold wet start too winter and a dry end
Member Since: May 21, 2006 Posts: 5091 Comments: 114756
1157. Levi32
The 12z GFS showed really nice timing with the SOI pulse spinning up a storm in the eastern Pacific in about a week and then forming a storm in the western Caribbean 5 days after that accompanied by a Cape Verde storm.
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1156. Drakoen
Quoting MiamiHurricanes09:
No signs of Earl through 156 hours on the 18z run.


GFS 12z
Member Since: October 28, 2006 Posts: 57 Comments: 29912
92L still has a defined mid level circulation.
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Quoting AstroHurricane001:


The remnants of Colin are flaring up again. When that new CDO collapses and starts setting off momentum toward the storm's surface rotation, that's when I'd re-label it a TS.

Hurricane Hunter Observations for 92L...Maximum surface wind found by aircraft...60 mph. WHAT!!!



no nhc fight for 92L any time soon
Member Since: May 21, 2006 Posts: 5091 Comments: 114756
1153. Levi32
Quoting TexasHurricane:


what does that mean?


It just means that the CFS thinks this will be the most powerful La Nina ever recorded, but it likely won't get that strong.
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Quoting thelmores:
I am starting to think Colin is Karen's Cousin! LOL


lol
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Quoting Drakoen:


If the GFS complete run verified we would be up to the F storm by August 20th.
No signs of Earl through 156 hours on the 18z run.
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The remnants of Colin are flaring up again. When that new CDO collapses and starts setting off momentum toward the storm's surface rotation, that's when I'd re-label it a TS.

Hurricane Hunter Observations for 92L...Maximum surface wind found by aircraft...60 mph. WHAT!!!
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Come on Colin.
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I am starting to think Colin is Karen's Cousin! LOL
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2. SUCCEEDING DAY OUTLOOK:
A. A 06/1800Z FIX ON COLIN IF STILL A VIABLE
SYSTEM NEAR 27.0N 69.0W.
B. A POSSIBLE LOW LEVEL INVEST AT 06/1500Z
NEAR 16.5N 84.5W.

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Quoting Levi32:
Holy snap....Some of the latest CFS member forecasts (blue lines) now predicting a La Nina of below -3.0!



what does that mean?
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Quoting Levi32:
Holy snap....Some of the latest CFS member forecasts (blue lines) now predicting a La Nina of below -3.0!




we see this go year round this year
Member Since: May 21, 2006 Posts: 5091 Comments: 114756
1144. Drakoen
Quoting Levi32:
After Colin and perhaps Danielle in the eastern Atlantic are out of the picture, we may have to wait for about 5 days to a week to see more action, which would be timed with the MJO coming into the Atlantic by mid-month and the SOI pulse coming across the Pacific. The eastern Pacific may try to spin up a storm before we get another one.


If the GFS complete run verified we would be up to the F storm by August 20th.
Member Since: October 28, 2006 Posts: 57 Comments: 29912
Quite true stormpetrol some how I am starting to see a circulation with 92L near 15N 75W
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1142. Levi32
Holy snap....Some of the latest CFS member forecasts (blue lines) now predicting a La Nina of below -3.0!

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1141. Drakoen
Quoting muddertracker:
Will a change in the llc mean a different track...or is it up and out no matter what center develops?


No this is still going to recurve
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1140. Levi32
After Colin and perhaps Danielle in the eastern Atlantic are out of the picture, we may have to wait for about 5 days to a week to see more action, which would be timed with the MJO coming into the Atlantic by mid-month and the SOI pulse coming across the Pacific. The eastern Pacific may try to spin up a storm before we get another one.
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Wow Colin does better in hostile conditions?
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92L maintains good cyclonic curvature. It also appears to be moving towards the WNW now.

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Quoting Drakoen:
This pass from 5 hours ago suggests that two centers did/do exist:



The question is which one is dominant. Recon will find that out.
Will a change in the llc mean a different track...or is it up and out no matter what center develops?
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1135. Levi32
12z ECMWF shows NAO going negative during the next 10 days, more from the Azores High pulling north than anything, but that will relax the trade winds and supports tropical development.

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1134. SLU
I must admit i'm one of those who verbally assaulted the new GFS model when it made its debut but to its credit it has done really well with Colin so far. The model showed a persistent WNW track north of the islands when even the ECMWF was confused going back and forth with Colin and even indicating that the system would open up into a trough while moving quickly WNW.

So thumbs up GFS!

It now shows another recurving system forming off the wave in the eastern Atlantic so let's see how it does then.

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1133. xcool
Link

go here .tkeith
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1131. Levi32
Quoting winter123:
Why are waves moving so fast this year? Warm water makes the trade winds faster?


No a strong Azores High does.
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i think 92L is going POOF
Member Since: May 21, 2006 Posts: 5091 Comments: 114756
Though 92L convection has warmed quite a bit its overall structure has improved in my opinion.
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Wow...the vorticity has really gone up around Colin!
wassup?!
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1127. Parkay
Quoting xcool:




Looks like a closed surface circulation in the last few frames. And one heck of a convective explosion just east of the COC.
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1125. Drakoen
This pass from 5 hours ago suggests that two centers did/do exist:



The question is which one is dominant. Recon will find that out.
Member Since: October 28, 2006 Posts: 57 Comments: 29912
i think 92L is weaking right now


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1123. 7544
did he stall ?
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Why are waves moving so fast this year? Warm water makes the trade winds faster?
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Quoting MiamiHurricanes09:
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.




is the F storm in there some where some where
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1117. HadesGodWyvern (Mod)
Philippines Atmospheric Geophysical Astronomical Services and Administration
Tropical Cyclone Bulletin #6
TROPICAL DEPRESSION DOMENG
5:00 AM PhST August 5 2010
=============================================

"Domeng" has weakened into a Tropical Depression as it continues to move towards Cagayan.

At 4:00 AM PhST, Tropical Depression Domeng located at 19.3°N 124.2°E or 240 kms southeast of Basco, Batanes has 10 minute sustained winds of 30 knots. The depression is reported as moving west southwest at 7 knots.

Signal Warning #1
==================

Luzon Region
-----------
1.Aurora
2.Quirino
3.Nueva Viscaya
4.Benguet
5.La Union
6.Mt. Province
7.Isabela
8.Ifugao
9.Kalinga
10.Apayao
11.Abra
12.Ilocos Sur
13.Ilocos Norte
14.Cagayan
15.Babuyan Islands
16.Calayan Islands
17.Batanes Group of Islands

Additional Information
========================
Public Storm Warning signals elsewhere now lowered.

Residents living in low lying and mountainous areas under signal # 1 are alerted against possible flash floods and landslides.

Meanwhile, a Low Pressure Area was estimated at 940 kms East of Luzon (16.5°N 132.5°E).

The public and the disaster coordinating councils concerned are advised to take appropriate actions and watch for the next bulletin alert to be issued at 11 AM today.
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Also evidence of the upper level anticyclone exists with the flow south of Colin's new convection explosion over eastern Caribbean Sea. The flow can be seen moving southwestward at the upper levels as cirrus blowoff move away from him. Also outflow is established on the southeast quadrant of the Colin remnants.
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1115. tkeith
1092. xcool 5:06 PM CDT on August 04, 2010

X could you post a link to that product?
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1114. SLU
Quoting Seflhurricane:
more than likely before calling it they will wait for recon to confirm


Yes I believe so.
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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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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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