CSU and TSR continue to predict a near-average hurricane season

By: Dr. Jeff Masters , 3:18 PM GMT on August 04, 2009

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A tropical disturbance embedded in the Intertropical Convergence Zone (ITCZ), near 9N 35W, is moving west at about 15 mph. The heavy thunderstorm activity associated with this tropical wave has changed little over the past 24 hours, and remains disorganized. This morning's QuikSCAT pass showed a moderate wind shift, but nothing resembling an organized surface circulation. Top winds were in the 20 - 30 mph range. Strong easterly winds are creating about 20 knots of wind shear over the wave, which is marginally conducive for development. The disturbance is about 300 miles south of the Saharan Air Layer (SAL), so dust and dry air should not hinder development over the next few days.

Given the disturbance's current lack of organization, combined with the presence of 20 knots of wind shear, any development should be slow to occur. The forecast wind shear along the storm's path over the next five days is predicted to remain at or below 20 knots, which should allow some slow development. Sea surface temperatures (SSTs) will warm from about 28°C to 29°C as the storm progresses westward. The GFS model has been indicating some development is possible in several of its runs over the past few days, but has not been consistent with this prediction. None of the other models show any development of the system. NHC is giving the disturbance a low (less than 30% chance) of developing into a tropical depression over the next two days, which is a good forecast. The GFS and ECMWF models predict the system will be approaching the northern Lesser Antilles Islands by Sunday. Both models forecast the development of a band of very high wind shear just to the north of the islands at that time, so the long-range survival of anything that might manage to develop is in doubt.

CSU forecast team continues to predict an average hurricane season
A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued August 4 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 10 named storms, 4 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 83% of average. 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 15 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is a step down from their June forecast, which called for 11 named storms, 5 hurricanes, and 2 intense hurricanes. Their April forecast called for 12 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast calls for a near-average chance of a major hurricane hitting the U.S., both along the East Coast (27% chance, 31% chance is average) and the Gulf Coast (26% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane (37%; 42% is average).

The forecasters noted that while sea surface temperature anomalies have increased in the tropical Atlantic and surface pressures have fallen in recent weeks, which normally would favor higher hurricane activity, the presence of El Niño conditions in the Eastern Pacific should counteract these influences. They forecast that the current weak El Niño event will strengthen to a moderate event by September:

El Niño events tend to be associated with increased levels of vertical wind shear and decreased levels of Atlantic hurricane activity. Tropical Atlantic sea surface temperatures anomalies have warmed somewhat since our early June prediction and surface pressures have fallen somewhat. But, the negative influences of El Niño-induced strong Caribbean Basin and Main Development Region vertical wind shear typically dominate over surface pressure and sea surface temperature in the tropical Atlantic.



Figure 1. Change in Sea Surface Temperature anomaly (in °C) between July 2009 and May 2009. Most of the tropical Atlantic has warmed, relative to normal, over the past 2 months. Image credit: NOAA/ESRL.

Analogue years
The CSU team picked four previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: weak to moderate El Niño conditions, and average tropical Atlantic and far northern Atlantic SSTs. Those four years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 1965, which had Category 3 Betsy that hit New Orleans; 1963, which had Category 4 Hurricane Flora that devastated Cuba; and 1957, which didn't have any hurricanes that hit hit land during the peak part of hurricane season. The mean activity for these four years was 9 named storms, 4 hurricanes, and 2 intense hurricanes--almost the same as the 2009 CSU forecast.

How accurate are the August forecasts?
The August forecasts by the CSU team have historically offered a skill of 45 -62% higher than a "no-skill" forecast using climatology (Figure 2). However, they are using a new forecast scheme this year, so it is difficult to judge how skillful this year's forecast might be.


Figure 2. Accuracy of long-range forecasts of Atlantic hurricane season activity performed at Colorado State University (CSU) by Dr. Bill Gray's team (colored squares) and Tropical Storm Risk, Inc. (TSR, colored lines). The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

August 2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) also issued a new forecast today, and have increased their numbers by 20% from their June and July forecasts. TSR is also calling for a near-average season, predicting 12.6 named storms, 6.5 hurricanes, 2.8 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 103% of average. Their June forecast called for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are slightly above the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TSR predicts a 40% chance of an above-average season, 44% chance of a near-average season, and a 19% chance of a below-average season, as defined by ACE index. TSR rates their skill level as 51% above chance at forecasting the number of named storms, 60% skill for hurricanes, and 44% skill for intense hurricanes. These are far higher skill numbers than the June ones: 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.8 named storms will hit the U.S., with 1.6 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these August forecasts for U.S. landfalls is 25% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.1 named storms, 0.5 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites one main factor for their increased forecast: higher sea surface temperatures than expected over the tropical Atlantic, due to the fact that the trade winds over the Atlantic should be slower than originally anticipated. Faster than average trade winds create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling.

The CSU and TSR groups are done making forecasts for the coming hurricane season, but NOAA is still due to put out an August update.

I'll have an update on Wednesday.
Jeff Masters

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Quoting StSimonsIslandGAGuy:
I don't recall any reputable blogger yesterday saying that the Atlantic wave was about to turn into Ana....


Key word being "reputable"
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8PM out, yellow circle still there.
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Even with all my doubts though, I would be quite surprised if the NHC suddenly dropped the yellow circle. Not a wise thing to do, by any means.
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This is going be Ana, no question, no doubt, a whistling duck just told me so! :)
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Quoting kmanislander:
The interesting thing about the QS pass this evening is that it caught the W edge of a low level circulation that is colocated with the 850 mb vorticity and the new convection we see firing near 10N 30W.

I wouldn't write this off just yet


Yep!
Member Since: June 29, 2009 Posts: 13 Comments: 5311
Quoting KYhomeboy:
LOL. Wow...yesterday people were certain of Ana forming...now today everyone is thinking it will "die." You can't expect to sway your opinion the second heavy convection develops, or sway it when it diminishes. What part of a normal cycle do people not get? This trend is typical of developing features. Give it some time..sit back and observe and stop making predictions based on an hour-to-hour infrared satellite loop!

Exactly!
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Currently Active Tropical Cyclones

* Current Active Cyclones



Last Updated 16 Minutes Ago

Atlantic* No Currently Active Cyclones

Eastern Pacific
Member Since: July 3, 2005 Posts: 423 Comments: 127805
Quoting kmanislander:
The interesting thing about the QS pass this evening is that it caught the W edge of a low level circulation that is colocated with the 850 mb vorticity and the new convection we see firing near 10N 30W.

I wouldn't write this off just yet


I agree
The yellow circle will NOT be dropped. And, how many times do we write systems off only to see them come back later. This still does need to be monitored for changes.
Member Since: June 29, 2009 Posts: 13 Comments: 5311
The interesting thing about the QS pass this evening is that it caught the W edge of a low level circulation that is colocated with the 850 mb vorticity and the new convection we see firing near 10N 30W.

I wouldn't write this off just yet
Member Since: August 19, 2006 Posts: 0 Comments: 15798
500mb vorticity:


700mb vorticity:




850mb vorticity:


New maps coming out in about 10 mins
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting KYhomeboy:
LOL. Wow...yesterday people were certain of Ana forming...now today everyone is thinking it will "die." You can't expect to sway your opinion the second heavy convection develops, or sway it when it diminishes. What part of a normal cycle do people not get? This trend is typical of developing features. Give it some time..sit back and observe and stop making predictions based on an hour-to-hour infrared satellite loop!



Member Since: July 3, 2005 Posts: 423 Comments: 127805
Quoting KYhomeboy:
LOL. Wow...yesterday people were certain of Ana forming...now today everyone is thinking it will "die." You can't expect to sway your opinion the second heavy convection develops, or sway it when it diminishes. What part of a normal cycle do people not get? This trend is typical of developing features. Give it some time..sit back and observe and stop making predictions based on an hour-to-hour infrared satellite loop!


I never said this was going to develop over the last 48 hours. Indeed, I had always had the long-term chances for tropical cyclogenesis at only 30 to 40%. My doubts today are not due to diurnal fluctuations evident in satellite imagery, but rather, a substantial increase in vertical shear in the system's long-term path. Models are calling for some rather unfavorable 200 mb winds, and as such, the system's long-term survival seems questionable.
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Quoting KYhomeboy:
LOL. Wow...yesterday people were certain of Ana forming...now today everyone is thinking it will "die." You can't expect to sway your opinion the second heavy convection develops, or sway it when it diminishes. What part of a normal cycle do people not get? This trend is typical of developing features. Give it some time..sit back and observe and stop making predictions based on an hour-to-hour infrared satellite loop!


It seems like it will always be this way, like people expect systems to form or fall apart in an instant and dont realize that there is a process that it goes through.

It is sad to see
GOES-12 Atmospheric Imagery

These images are primarily for use in tropical storm monitoring. There are several areas to choose from providing a large-scale view of the Atlantic, down to the Gulf of Mexico. During hurricane season, the hurricanes page provides a variety of GOES atmospheric products to help monitor the active storms.


Member Since: July 3, 2005 Posts: 423 Comments: 127805
LOL. Wow...yesterday people were certain of Ana forming...now today everyone is thinking it will "die." You can't expect to sway your opinion the second heavy convection develops, or sway it when it diminishes. What part of a normal cycle do people not get? This trend is typical of developing features. Give it some time..sit back and observe and stop making predictions based on an hour-to-hour infrared satellite loop!
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Quoting Drakoen:


Little model support for this mess, very doubtful:



I was stretching and reaching Sir Drak,..lol
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Quoting cyclonekid:
Am scared for Yellow Circle now...maybe dropped. :((

The vorticity seems to be increasing, but the convection isn't really there.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
The system is broad but still has potential

I doubt the yellow circle gets taken down
There is, at best, a broad and highly disorganized area of vorticity associated with the system, and it is likely primarily at 500-700 mb. Some weak 850 mb vorticity is appearing on CIMSS data, but not enough to impress me.
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Quoting sammywammybamy:
Possiblity of a Hawai hit isnt that bad

If it does it will be a weak hurricane at most..water temps don't support sustainable growth.
Member Since: June 21, 2007 Posts: 10 Comments: 1657
Am scared for Yellow Circle now...maybe dropped. :((
Member Since: July 14, 2009 Posts: 51 Comments: 1727
Wrf model weakens it completely.But i have a different opinion slightly decreasing shear next 2 to 3 days may give a 20% of forming increase chance from 10% yesterday.
It's not "firing in all cylinders" anymore :(
Member Since: October 28, 2006 Posts: 57 Comments: 30157
Quoting AllStar17:
TampaFLUSA -- If the NHC mentions something that has potential for development, the basin is not quiet...as there is potential for a cyclone to form.

The potential is always there....but putting down a well respected Met is not going to get anywhere.
Member Since: June 21, 2007 Posts: 10 Comments: 1657
I'm not as impressed with this wave as I was just yesterday. Long-term chances of survival are quite low.
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Quoting Patrap:
Looks like maybe,er maybe the Broad low will be the Dominate entity in 24-48.


Little model support for this mess, very doubtful:

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GOES-12 WV False Color,Atlantic,LARGE image
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Looks like maybe,er maybe the Broad low will be the Dominate entity in 24-48.
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yes its right. I think once it reached 45W we can judge better. Now keep and eye
Member Since: July 21, 2009 Posts: 0 Comments: 552
No threats in the Atlantic is just the way it is,theres not even a invest.

Lets be thankful the season has brought minimal havoc on the Basin.
May it continue for those still in recovery mode.

Member Since: July 3, 2005 Posts: 423 Comments: 127805
QuickScat caught a broad low level circulation back near 31W.
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TampaFLUSA -- If the NHC mentions something that has potential for development, the basin is not quiet...as there is potential for a cyclone to form.
Member Since: June 29, 2009 Posts: 13 Comments: 5311
Fair weather in the Atlantic but things could get active by mid to late August with a decent MJO coming around and lasting 2-3weeks.
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784. IKE
2100UTC 850mb vort....still a strong vort at 11N and 30W. Latest NOGAPS strengthens that vort and moves it west.


Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting hunkerdown:
WU blog.

lol WU University
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Quoting TampaFLUSA:

Umm yea..and what training do you have?
WU blog.
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Quoting AllStar17:


Dr. Lyons is ridiculous. No mention....atlantic is quiet. If he looked at the NHC website, they are not saying it is quiet. They have mentioned an AOI. This guy is brutal...and he would get completely burned if this formed and posed a threat to land as a strong system.

Umm yea..and what training do you have?
Member Since: June 21, 2007 Posts: 10 Comments: 1657
Quoting AllStar17:


Dr. Lyons is ridiculous. No mention....atlantic is quiet. If he looked at the NHC website, they are not saying it is quiet. They have mentioned an AOI. This guy is brutal...and he would get completely burned if this formed and posed a threat to land as a strong system.
The ATL, for the most part, is quiet. The "AOIs", as you call them, are in the ITCZ. I would put the %s of development slim and possibly fading.
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Quoting IKE:


Too soon to know for sure. Hurricane center has the system weakening by Sunday to a 65 knot storm SE of Hawaii.

Plus the water temps cool down to around 75ish...
Member Since: June 21, 2007 Posts: 10 Comments: 1657
778. IKE
Quoting clwstmchasr:
Steve Lyons...Tropical update..."fair weather out in the Atlantic."

It think he does that just to enrage us!

Did he talk about how great the surfing is in CA:)


He was pressed for time. TWC is spending a lot of time talking about flooding in Louisville,KY.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
777. IKE
Quoting Chicklit:

This is the same crew whose Chief Met says "no land affected" by Felicia and her brother Enrique. How is HI looking? Do you think the Island chain will be spared?


Too soon to know for sure. Hurricane center has the system weakening by Sunday to a 65 knot storm SE of Hawaii.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Tropical Storm Enrique Wind Field



Hurricane Felicia Wind Field

Member Since: July 3, 2005 Posts: 423 Comments: 127805
Quoting Chicklit:

This is the same crew whose Chief Met says "no land affected" by Felicia and her brother Enrique. How is HI looking? Do you think the Island chain will be spared?
From a cane, yes...from sort of "impact", probably not. Obviously surf will be up and possibly gusty winds. Although the trades are gusty regardless this time of year, gusts at or near tropical storm strngth is not uncommon.
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Quoting IKE:
Steve Lyons...Tropical update..."fair weather out in the Atlantic."


Dr. Lyons is ridiculous. No mention....atlantic is quiet. If he looked at the NHC website, they are not saying it is quiet. They have mentioned an AOI. This guy is brutal...and he would get completely burned if this formed and posed a threat to land as a strong system.
Member Since: June 29, 2009 Posts: 13 Comments: 5311
Quoting TampaFLUSA:

Rm34667 was mistaken, he was referring to a different disturbance..Dr M said Dean WOULD form.

Okay, I'm not supposed to be messing around in this now anyway as I'm in critical meltdown with my projects. Will check back later!
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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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