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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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...
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Quoting cyclonekid:
Do the negative numbers show an anticyclone...Just got link today..don't really know much.


It means decreasing shear, which may or may not be associated with an anticyclone. In most cases, in with this one, it is not associated with an anticyclone
Quoting Drakoen:
Firing in all cylinders!!! LMFAO! Please.


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 intense stuff going on in the west pac check out the 12z CMC with Morakot.
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Experimental forecast Tropical Cyclone Genesis Potential Fields


This page presents operational model fields that are being used in a study examining their
forecast ability for tropical cyclogenesis in the eastern Pacific and northern Atlantic basins.

Please note that these products are experimental and not official forecasts. For official forecasts in the U.S.,
please refer to the National Weather Service and National Hurricane Center.

Pleaes note that effective 22 May 2009, UKMO will no longer be supplying their high resolution UKMET
output for plotting here.

Model data last updated Tue Aug 4 18:44:49 UTC 2009.
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366. HadesGodWyvern (Mod)


thought the dry air was always colored brown.. thundercloud
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It continues to suffer from 20-30 knots of wind shear.
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Do the negative numbers show an anticyclone...Just got link today..don't really know much.
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East.Pacific

HU-FELICIA.65kts-987mb-122N-1261W
TS-ENRIQUE.50kts-998mb-148N-1178W

West.Pacific
TS-MORAKOT.50kts-985mb-224N-1337E
TD-GONI.45kts-989mb-218N-1130E
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Quoting presslord:



actually....it's the most reliable "model"...


By who?

Link
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Quoting btwntx08:

it says 1500 utc more than 4 hrs old....ww12 is right we are still waiting for the new one to out


Again the East Atlantic one is updated, I am not talking about the Central Atlantic one
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New maps should come out about 3:40
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EP, 08, 2009080418, , BEST, 0, 122N, 1261W, 65, 987, HU,
Member Since: August 2, 2007 Posts: 19 Comments: 19234
354. Relix
Darn, its sticking so much to the South that its starting to scare me here in PR. Those low laying ones are the worst type for us.
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Quoting cg2916:

There's a bunch of shear in the Caribbean.


Maybe not for long

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Just dropping in to post a link to a weather buoy at 8N 38W that the feature will soon be at for those who are interested.

Station 13009
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Quoting tropicfreak:


What is the XTRP?

A computer model that takes the movement in the last 6 hours and shows where it would go if it didn't change track at all.
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Shear is 20 knots right now and its coming out of the east, so shear is a bit of an issue but not much

Also as was stated before, a few forecast models say that an anticyclone will form over or near this system in the next day or two
Quoting tropicfreak:


At least 20 kts.

That map is 4 hours old
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Quoting tropicfreak:


What is the XTRP?


it's simply an extrapolation of a systems' current course....it's never wrong...
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I do not think enrique will make it dry air is intruding and will get to the center shortly. I think it will dissipate rapidly over the next 24-48 hours

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 04 AUG 2009 Time : 183000 UTC
Lat : 15:01:44 N Lon : 117:49:56 W


CI# /Pressure/ Vmax
3.8 / 991.9mb/ 61.0kt


Final T# Adj T# Raw T#
(3hr avg)
3.5 3.3 3.3

Latitude bias adjustment to MSLP : +2.1mb

Center Temp : -48.3C Cloud Region Temp : -51.9C

Scene Type : UNIFORM CDO CLOUD REGION

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : EAST PACIFIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : FLAG

****************************************************
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At least 20 kts.
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Quoting bajelayman2:
Looking at the latest loop, I would go with the wave holding a lower than originally forecast track.

However, the loop seems to indicate that the wave still appears to be in a life and death fight with shear, which would indicate at the very most, slow development, or none at all.

Those who have been predicting a Caribbean Sea development, if it gets that far, could be right.

There's a bunch of shear in the Caribbean.
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Quoting cg2916:

First, they have models on it?
Second, as you probably know, the XTRP is the most unreliable model ot there.


What is the XTRP?
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Quoting largeeyes:
It's losing convection, that's for sure. Dry air?

Looks more like shear.
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Looking at the latest loop, I would go with the wave holding a lower than originally forecast track.

However, the loop seems to indicate that the wave still appears to be in a life and death fight with shear, which would indicate at the very most, slow development, or none at all.

Those who have been predicting a Caribbean Sea development, if it gets that far, could be right.
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341. HadesGodWyvern (Mod)
looks like it thundercloud

NHC Tropical Cyclone Guidance has sustained winds at 65 knots with a central pressure of 987 hPa
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Quoting cg2916:

First, they have models on it?
Second, as you probably know, the XTRP is the most unreliable model ot there.



actually....it's the most reliable "model"...
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Quoting Thundercloud01221991:
Felicia is a Hurricane

http://cimss.ssec.wisc.edu/tropic2/real-time/adt/adt.html

Not surprised. And this proves it:
EP, 08, 2009080418, , BEST, 0, 122N, 1261W, 65, 987, HU, 64, NEQ, 20, 20, 20, 20, 1007, 180, 20, 0, 0, E, 0, , 0, 0, FELICIA, M,
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It's losing convection, that's for sure. Dry air?
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Quoting cg2916:

So are you.



yes....South Carolinian...not 'Carolinian'...
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Quoting weatherwatcher12:
The shear map is not out yet


The East Atlantic one is
The shear map is not out yet
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Quoting presslord:
OMG!! The 'extrap model' takes it right over my house!!!!!!!!!

First, they have models on it?
Second, as you probably know, the XTRP is the most unreliable model ot there.
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Felicia is a Hurricane

http://cimss.ssec.wisc.edu/tropic2/real-time/adt/adt.html
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hey everyone hows it going? i think our system has a long road ahead of it but it does have pretty good circluation...we shouldn't write off anything with favorable conditions ahead of it...it has alot of work to do though
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It sure seems like it would progress further than 40W in three days time.
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Quoting presslord:



no....no....no....

You are a South Carolinian!!!!!!!!!!!!!!!!!!!!!

So are you.
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OMG!! The 'extrap model' takes it right over my house!!!!!!!!!
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Yes the convection is still present but its very small and overall still looks like a mess down there. We'll see what it does towards sunset and overnight.
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Quoting presslord:



no....no....no....

You are a South Carolinian!!!!!!!!!!!!!!!!!!!!!


Thats twice in 2 days.........LOL
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326. HadesGodWyvern (Mod)
Difference in intensity with Tropical Storm Goni (Jolina)

+ Hong Kong (HKO/10-min avg): 95 km/hr (50kts)
+ Korea (KMA/10-min avg): 85 km/hr (45kts)
+ USA (JTWC/1-min avg): 75 km/hr (40kts)
+ Beijing (NMC/2-min avg): 75 km/hr (40kts)
+ Taiwan (CWB/10-min avg): 65 km/hr (35kts)
+ Japan (JMA/10-min avg): 65 km/hr (35kts)
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Quoting 19N81W:
so 456 you think its going to go due north or is that another Low?


It's the same low put the ECMWF takes it NW. Trust me, until a define center forms, the models are not initializing very well.

The models have been calling for development for a week now but the track has not verified thus far. Last week they had the disturbance at about 14N at 33W, but in actuality at 33W, its below 10N. that's a large difference.
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Quoting StormW:
EUMETSAT 1845Z LOOP

Once again, convection in the center, maybe organzing, maybe.
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A little further West...No real surprise as long as its embedded within the ITCZ.....it will continue to follow.
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Shear map is out, shear continues to decrease

Huge anticyclone to the systems SE

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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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