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 19N81W:
what the heck happened?
just one of those seasons I guess...


nothing happened, NHC is acknowledging it now

structure is better than last night
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There are some outflow boundaries around the high pressure ridge at 47W/12N, 54W/14N, and 52W/12N. They do seem close to stationary which would indicate a good sign of instability in the region that the disturbance at 37W/9N is moving into.
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http://www.ssd.noaa.gov/goes/east/catl/loop-vis.html

is the circulation i see still at the mid levels because it appears as if it might be trying to work its way down to the surface
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what the heck happened?
just one of those seasons I guess...
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Quoting weatherwatcher12:
Shear looks to be decreasing around the blob.Am I wrong?


Also several forecast models are forecast an anticyclone to develop near or over the area
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Quoting CybrTeddy:


This is why your 'hurricane authority' is mostly wrong. Felicia could be our first US Landfall of the season.


...ya know...

That is an excellent point...and one that's easy to forget...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
Quoting caneswatch:


Mikatnight, you're not the only one who's nervous in Palm Beach County. I think this is the year we get hit by a Category 4 or 5.


Thats like saying I know Im going to win the lottery this year I know it.lol
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Any ideas why they missed the 12Z East Atlantic Imagery?
The 18Z should be out in about 35 min or so.
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Shear looks to be decreasing around the blob.Am I wrong?
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Quoting stoormfury:
456 where is the possible centre of the catl disturbance


based on visible images 32-33W
Member Since: July 24, 2005 Posts: 407 Comments: 19076
161. IKE
Look at a visible loop of the blob in the EATL, you can see higher cloud tops being blown from east to west.

20 knots of shear.....

Member Since: June 9, 2005 Posts: 23 Comments: 37860
The fact that 1965's an Analogue year concerns me.
Betsy hit Florida and New Orleans as a Category 3 with peak as a Category 4 in the GOMEX
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156. That is a stupid comment to make.
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456 where is the possible centre of the catl disturbance
Member Since: August 22, 2006 Posts: 0 Comments: 2722
Quoting caneswatch:


Mikatnight, you're not the only one who's nervous in Palm Beach County. I think this is the year we get hit by a Category 4 or 5.



MAN, I'm moving away from you two, lol. Wasn't the scare from IKE last year enough?
Quoting mikatnight:
Anyway, I'm stickin' with my 8-4-2 prediction (based on historical graphs). Don't know why, but for some reason I'm nervous as hell this year. I know there's no real scientific explanation, yet I remain concerened that the pattern of strikes from the 40's will reoccur and Palm Beach County will get nailed. Also, I noticed that the CSU team's analogue years didn't appear to include storms from before 1950.


Mikatnight, you're not the only one who's nervous in Palm Beach County. I think this is the year we get hit by a Category 4 or 5.
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The ITCZ is nudging a few degrees north.
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TWD = Tropics plus TV gone bad.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
I think we might see Ana soon.
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I'm not sure Shear ever relaxes in the ITCZ does it....the Convergence of the Northern and Southern Hempishere does it allow for relaxed shear.....i don't know...but, i didn't think so.
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Quoting Chicklit:
The hurricane report on my Blackberry (sponsored by the Weather Channel)this morning said the EPac systems are "no threat to land."
Wondering where they got that when it appears the Hawaiian Chain is within range. Correct?


This is why your 'hurricane authority' is mostly wrong. Felicia could be our first US Landfall of the season.
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150. IKE
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting StormW:


Now near 32W


Now that the Easterly shear has slacken some... it might have a chance to consolidate better later tonight.
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850mb vorticity is showing the blob of storms is racing ahead of the Lower Levels trying to form. That is caused by the ITCZ.
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Quoting StormW:


Now near 32W


yup agreed, 2pm TWD is based on the surface analysis from 6 hours ago, not now. Since then the low level circulation has moved further west

I have a question, why does the 2pm TWO say that this area is a tropical wave, but the TWD says it isnt a tropical wave?
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2PM TWD

AN ACTIVE SURFACE TROUGH IS ALONG 34W/35W S OF 12N. WHILE IT IS
CURRENTLY NOT ANALYZED AS A TROPICAL WAVE...IT MAY BE
TRANSITIONED TO ONE ON FUTURE SURFACE ANALYSIS. MID-LEVEL
CYCLONIC CIRCULATION IS NEAR THE TROUGH AXIS SUPPORTING
SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 7N-10N
BETWEEN 33W-37W. HOWEVER...VISIBLE SATELLITE IMAGERY AND
QUIKSCAT DATA AROUND 0800 UTC INDICATES THAT LOW LEVEL
CYCLONIC CIRCULATION IS FARTHER E AROUND 30W.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Just completed my tropical update if anyone would like to view.
TampaSpins Tropical Update....
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AN ACTIVE SURFACE TROUGH IS ALONG 34W/35W S OF 12N. WHILE IT IS
CURRENTLY NOT ANALYZED AS A TROPICAL WAVE...IT MAY BE
TRANSITIONED TO ONE ON FUTURE SURFACE ANALYSIS. MID-LEVEL
CYCLONIC CIRCULATION IS NEAR THE TROUGH AXIS SUPPORTING
SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 7N-10N
BETWEEN 33W-37W. HOWEVER...VISIBLE SATELLITE IMAGERY AND
QUIKSCAT DATA AROUND 0800 UTC INDICATES THAT LOW LEVEL
CYCLONIC CIRCULATION IS FARTHER E AROUND 30W.
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12Z GFS and CMC

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Member Since: March 19, 2009 Posts: 0 Comments: 1421
I see some convection firing off in the system.
Lets just see what the 8 PM TWO says, actually more like the 8 AM TWO tomorrow. If we do get to orange I think its possible by 8 PM tomorrow if the system holds up.
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139. HadesGodWyvern (Mod)


about to make landfall..
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I agree with the NHC, that the system is disorganize per visible images but I also agree slow development is still possible based on favourable enviromental conditions.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
No real change in the TWO.
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136. HadesGodWyvern (Mod)
Tropical Cyclone Bulletin

Here is the latest Tropical Cyclone Bulletin issued by the Hong Kong Observatory.

The No. 8 Southeast Gale or Storm Signal is in force.

This means that winds with mean speeds of 63 kilometres per hour or more are expected from the southeast quarter.

At 1 a.m., Severe Tropical Storm Goni was centred about 130 kilometres west-southwest of Hong Kong (near 21.7 degrees north 113.1 degrees east) and is forecast to move west or west-northwest at about 10 kilometres per hour towards the western coast of the Pearl River Estuary.
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000
ABNT20 KNHC 041733
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT TUE AUG 4 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

DISORGANIZED SHOWERS AND THUNDERSTORMS SEVERAL HUNDRED MILES
SOUTHWEST OF THE CAPE VERDE ISLANDS ARE ASSOCIATED WITH A TROPICAL
WAVE. SIGNIFICANT DEVELOPMENT...IF ANY...OF THE SYSTEM IS EXPECTED
TO BE SLOW TO OCCUR AS THIS WAVE MOVES TO WEST AT ABOUT 15 MPH.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Drakoen:
Looks like any ordinary tropical wave deeply embedded within the ITCZ


I kind of agree with you but some experts are saying that this storm can have some potential in further development. We would have to wait and see if that occurs.
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Looks like any ordinary tropical wave deeply embedded within the ITCZ
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Good afternoon Weather
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Quoting CaribbeanWave:
Hello Everyone,

I haven't been on this blog since the last hurricane season. There was nothing to report but I have a gut feeling that this area of disturbance in the Atlantic is something to watch for. The only concern for this system, like Jeff Master said, is the wind 20 knt wind shear that can inhibit in significant development.

Lets keep our eyes on it.


Thank God you told them that! I was afraid they would just ignore it.
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I wonder if Felicia will inhibit Enrique from forming further or will it slow Enrique, by cooling the waters behind it and stealing available mositure. I know when two storms are close to each other there is a tendicency for one to get the short end of the stick?
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129. 7544
Quoting BurnedAfterPosting:
This system did take a major step, NHC is recognizing it now and they werent last night, also the NHC appears to be initiating now as a tropical wave.


agree this one may go oiut to sea the second one coming into play may be the one to watch
Link
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Good Afternoon,

I see our disturbance is holding its own

Tropical Update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
This system did take a major step, NHC is recognizing it now and they werent last night, also the NHC appears to be initiating now as a tropical wave.
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Member Since: August 1, 2006 Posts: 28 Comments: 3716
No matter how short lived they may be, right now both waves look pretty good:


Link
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Quoting WxLogic:
Based on 15Z VORT Charts... vorticity is starting to increase at lower levels (850MB to 700MB) with a 500MB still present but elongated still.

SAT images are starting to show this cyclonic turning... although convection has wane for now... it will have the opportunity to recover during DMAX now that DMIN is going to be peaking soon.


agreed as StormW and 456 both said, while convection has waned, it is better organized overall compared to last night.
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Quoting StormW:
TROPICAL WEATHER SYNOPSIS AUG 04, 2009 ISSUED 11:15 A.M. EDT


Thanks Storm, great update.
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Quoting cg2916:
Is it me or is the wave falling apart?

Looks like it's in a higher shear area. Probably will wax and wane over the next few days as it encounters shear, dust, but nothing is really strong enough at this point, IMO, to wipe it out. Persistence appears to be the key word this week.
Member Since: July 11, 2006 Posts: 14 Comments: 11410

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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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