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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422. IKE
1800UTC vorticity @ 850mb's shows the vort up near 11 north and 30 west....

I see a spin(not as noticeable as yesterday), near 9N and 36W....

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409:Patrap,

So is this saying that SST's may be more important than shear???
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Schoolyard tactics are the most embarrasing things observed here today.

In the Buisness of Tropical Blogging,one should always check their ego's at the Hatch/door.
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Quoting atmoaggie:


Agreed. The only less than friendly remarks I see by reading back were from others (unless, of course, big modifications were made).


...and....disagreeing about the tropics IS discussing the tropics...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
It looks like the ITCZ.
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New shear map out.

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416. HadesGodWyvern (Mod)
The No. 3 Strong Wind Signal has been issued at 3:40 a.m. to replace the No. 8 Southeast Gale or Storm Signal.

---
Well, Goni appears to be moving away from Hong Kong region.
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Quoting WxLogic:


Hehe... not quite a good question to ask quite yet. Keep in mind that shallow systems will tend to head W while deeper system tend to recurve more to the right (North Hemisphere) so basically turn poleward.


That is correct......if it does not develop much it heads WEST!
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Quoting hurricanejunky:
I don't quite understand why everyone is coming down on Drak so hard. I mean he didn't use profanity or lash out at anyone in an attack. He was just stating a different point of view in his forecast.


Agreed. The only less than friendly remarks I see by reading back were from others (unless, of course, big modifications were made).
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Quoting TampaSpin:
If it does not seperate from the ITCZ soon then the Windward Islands may have to deal with this.....It would seperate just before approaching!


Just like Felix did, that wasn't a fun one for them.
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It has a tropical storm structure...lol

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I wanna see it get out of the ITCZ...the ITCZ seems to be a crutch for these things and if it can hang together and persist outside of there then it could get interesting. It does seem to still be firing some convection around the bottom of whatever spin its got.
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Funny, remember the last couple of years, the hurricanes that waltzed right through shear?

Katrina and others, cannot remember which?
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Tropical Cyclone Heat Potential
NOAA Home AOML Home PhOD Home



The real-time estimates and data distribution of AOML TCHP fields have been discontinued.
Introduction

The intensification of tropical cyclones involves a combination of different favorable atmospheric conditions such as atmospheric trough interactions and vertical shear, which lead to good outflow conditions aloft. As a result of this, inflow conditions in the near-surface layer are enhanced. Clearly, as this process continues over the scale of the storm, the upper ocean provides the heat to the atmospheric boundary layer and the deepening process. In this scenario, the upper ocean thermal structure has been thought to be a parameter that only played a marginal role in tropical cyclone intensification. However, after a series of events where the sudden intensification of tropical cyclones occurred when their path passed over oceanic warm features, it is now being speculated that it could be otherwise. While the investigation of the role of these rings and eddies is a topic of research in a very early stage, preliminary results have shown their importance in the intensification of hurricane Opal (Shay et al, 2000). Therefore, the monitoring of the upper ocean thermal structure has become a key element in the study of hurricane-ocean interaction with respect to the prediction of sudden tropical cyclone intensification. These warm features, mainly anticyclonic rings and eddies shed by the Loop Current, are characterized by a deepening of several tens of meters of the isotherms towards their centers and with different temperature and salinity structure than the surrounding waters
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for gods sake can we stop the bickering over one and the other GET OVER IT we need to be discussing the tropics lots to talk about remember you can get banned for getting off topic
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It's nice to see we are having a very very slow season and hope this trend continues and everyone stays safe
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If it does not seperate from the ITCZ soon then the Windward Islands may have to deal with this.....It would seperate just before approaching!
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Quoting mobilegirl81:
IF there is development, where will it go?


Hehe... not quite a good question to ask quite yet. Keep in mind that shallow systems will tend to head W while deeper system tend to recurve more to the right (North Hemisphere) so basically turn poleward.
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Quoting Drakoen:


Morakot is a monster on the CMC.


Regardless Globals have a trof near the islands which would initiate a recurve possibly out to sea with the atlantic disturbance.
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i am back what is new with our tropical disturbance in the central atlantic
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Quoting hurricanejunky:
I don't quite understand why everyone is coming down on Drak so hard. I mean he didn't use profanity or lash out at anyone in an attack. He was just stating a different point of view in his forecast. It's not like he's WeatherStudent proclaiming to know something about forecasting when he doesn't. He is, in fact, knowledgeable. I understand we want to maintain 100% accuracy but right now when discussing a tropical wave that is disorganized (it's a wave after all!) I don't know that 100% accuracy is as big a deal. If we're talking about a cat 4 hurricane bearing down on somewhere then accuracy is absolutely critical. I think it's a little extreme to put the guy on ignore for a difference of opinion. On the flip side, Drak has been known to lack people skills at times but sometimes that can also be attributed to intolerance for those who are less (sometimes MUCH less) knowledgeable than him. Just my thoughts...
I don't quite understand how you can defend one person and slam another in the same sentence. Seems like you show the same bias as the people who put drak on ignore. Besides have you never seen draks posts where he keeps track of the number of people on his ignore list. His opinions don't bother me nor do anyone's, but don't be a hypocrite and contradict what you're saying with what you're saying.
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Looking at the surface map.......no comment.
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The GFS forecast has not verified from yesterday.
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Quoting Weather456:
Nice structure



See naked swirl at 44 and 13 degrees. Just thought it was interesting...
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Tropical Storm Risk (TSR)
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Good thing there is some shear there, from what the loop shows, it is obviously trying to 'wrap' (ha...layman's terms) and tighten up, but the shear is interfering.

We'll see tomorrow am. I'll check first thing.
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.
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Quoting extreme236:
Still rather dry but not as bad as its been.



The ITCZ is helping to moisten the environment around it or in front of it. Seems to be holding its own, DMIN's kicking in. It wouldn't be a shocker to see this with deep convection tonight again.
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Ctrl Atl Wave Surface Obs Last 3 hours:

Agree that surface pressure falls are to the E, maybe too far.
I do see now how much harder a time this persistent thunderstorm is having with the shear than a real system would.
Still watching. Trying not to "cast".
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....StormVI . Com *Live....
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IF there is development, where will it go?
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Nice structure

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Quoting StormW:


Correct.

Thanks
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Quoting extreme236:
Still rather dry but not as bad as its been.



That still pic makes the system look like a Tropical Storm lol, looks pretty decent I would say
According to CIMSS the mid level circulation at 850mb is still at 10N 30W.
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Still rather dry but not as bad as its been.

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Quoting Barbados:
When did the yelow circle appear?


8am this morning
Afternoon everyone.

It sure looks like it could get interesting in the next few weeks.

12z CMC - 144hours

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Quoting StormChaser81:


By who?

Link


What I mean is...the course is what the course is...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
Quoting hurricanejunky:
I don't quite understand why everyone is coming down on Drak so hard. I mean he didn't use profanity or lash out at anyone in an attack. He was just stating a different point of view in his forecast. It's not like he's WeatherStudent proclaiming to know something about forecasting when he doesn't. He is, in fact, knowledgeable. I understand we want to maintain 100% accuracy but right now when discussing a tropical wave that is disorganized (it's a wave after all!) I don't know that 100% accuracy is as big a deal. If we're talking about a cat 4 hurricane bearing down on somewhere then accuracy is absolutely critical. I think it's a little extreme to put the guy on ignore for a difference of opinion. On the flip side, Drak has been known to lack people skills at times but sometimes that can also be attributed to intolerance for those who are less (sometimes MUCH less) knowledgeable than him. Just my thoughts...



Thank You~
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Quoting BurnedAfterPosting:


Again the East Atlantic one is updated, I am not talking about the Central Atlantic one


Indeed... compared to the 15Z... the 18Z shows a more impressive 850MB VORT MAX. and gaining latitude a bit as it moves further W.

But the 18Z graphics for the CATL should give a better view at how is evolving or decaying.
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When did the yellow circle appear?
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Judging the satellite view, looks like the disturbance in the atlantic is fluxuating just like storms do when they go through phases of growth.
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Shear should not be much of a factor if it does die it will be because other factors like dry air has gotten to it first shear is marginally favorable at 20 kts i've seen storms develop in worse
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Quoting StormW:


No...the negative values indicate how much the shear values have decreased in the past 24 hours.
in knots?
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Quoting btwntx08:

anyways i'm going with catl one which it will be relased shortly


thats fine, but they show the same thing, the EATL one goes out to 40W
TROPICAL DISCUSSION - INTERNATIONAL DESKS


OUTLOOK: MEDIUM RANGE GUIDANCE IS SHOWING A GRADUAL TRANSITION ON
THE NORTHERN PORTIONS OF THE DOMAINS. ON DAYS 04-05...THE RIDGE
OVER THE WESTERN USA WILL RELOCATE TO THE EASTERN USA/WESTERN
ATLANTIC. IN-TANDEM...AN UPPER LEVEL TROUGH WILL THEN ESTABLISH
OVER THE WESTERN ATLANTIC TO NORTH OF THE ISLANDS. DOWNSTREAM FROM
THIS TROUGH...A RIDGE WILL GRADUALLY BUILD/ESTABLISH OVER THE
EASTERN ATLANTIC TO THE NORTH OF 20N. THIS CHANGE WILL COINCIDE
WITH AN INCREASE IN THE MJO...WHICH SHOULD LAST FOR TWO TO THREE
WEEKS. THIS WILL BRING US CLOSER TO THE TYPICAL/MORE SEASONAL
CLIMATOLOGICAL PATTERN OVER THE DOMAIN...AND LIKELY MAKE IT MORE
FAVORABLE FOR TROPICAL CYCLONE FORMATION.
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Quoting hurricane23:


Yea... i wouldn't quite call that firing in all cylinders,this is still a very weak circulation/disturbance.Dry air still looks like it will be an issue for the time being along with 15-20kts of easterly shear.Per latest NHC discussion any weak surface circulation appears to be around 30west.

Pretty intence stuff going on in the west pac check out the 12z CMC with Morakot.


Morakot is a monster on the CMC.
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Hurricane/Typhoon Tracker

The Hurricane/Typhoon Tracker is currently limited to storm track data
from 2007 through present

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I don't quite understand why everyone is coming down on Drak so hard. I mean he didn't use profanity or lash out at anyone in an attack. He was just stating a different point of view in his forecast. It's not like he's WeatherStudent proclaiming to know something about forecasting when he doesn't. He is, in fact, knowledgeable. I understand we want to maintain 100% accuracy but right now when discussing a tropical wave that is disorganized (it's a wave after all!) I don't know that 100% accuracy is as big a deal. If we're talking about a cat 4 hurricane bearing down on somewhere then accuracy is absolutely critical. I think it's a little extreme to put the guy on ignore for a difference of opinion. On the flip side, Drak has been known to lack people skills at times but sometimes that can also be attributed to intolerance for those who are less (sometimes MUCH less) knowledgeable than him. Just my thoughts...
Member Since: Posts: Comments:

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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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