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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As stated by both the NHC & Dr. Masters, any development will be slow to occur with the tropical wave off the coast of Africa. You won't miss anything if you take a peek at the satellite images every 4 hours or so. No point in sctutinizing every frame 24-7.

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Quoting Stormchaser2007:
Impressive...


If that was in the Atlantic/Caribbean, this blog would freeze up!
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SHIPS take Felicia to Category 2 strength:

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Impressive...

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Quoting extreme236:


Based on?

just watching the latest CATL sat vis loop, it appears to a spin that area at least to me , thats all, even though the quikscat showed strong winds, to my untrained eye I can'tsee what I would call a defined closed low level circulation.
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ghcc loop
You will need to manual refresh
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Disorganized mess in the ITCZ this afternoon.
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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.


Don't tell me..... you live in Palm Beach county, right? lol
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IND is about to get hit by 65 mph winds at least
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62. IKE
Break in the ridge on 12Z GFS @ 120 hours...trough should pull the yellow circle...into the north Atlantic...

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Good one #57.
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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.
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59. IKE
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Blog Update
Reflector site for those at work, which includes Weather456, daily update.


AOI

AOI
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Interesting blog Doc, especially the Change in Anomaly graphic & the Analog years. I understand analogs don't mean we get the same storms as the patterns will diverge from those of tha analog seasons with time, and that it is a "timing thing" as to where & when a developing storm fits in with the oscillations in the pattern, but is is suggestive of a tendency for similar tracks/intensities.

Some may have watched TCs grow, move & die for many years, and while they don't retain it all like the computerized records/models, they probably remember some component of the patterns.
I never minded the "casters", up, down, or sideways (predictions based on a "gut feeling"/otherwise unsupported or unstated) as they got the idea from somewhere. It is their mind's interpretation of the current situation based on their past experience (different for everyone), tempered by how the information here and elsewhere is coming across.
The human brain is still in many respects superior to all the computing power behind the models (how long that remains true is hard to tell).
That being said, I'm still going to wait for the NHC to tell me when it is time to fill the bath tub, or leave.
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Quoting stormpetrol:
I think there is developing low near 8.5N/33.5W, jmo


Based on?
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I think there is developing low near 8.5N/33.5W, jmo
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Hi all,

Thanks to the Dr. for his usual pragmatic update. Here's a cool satellite link. Full disk loop, so takes a bit to load:Link
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very strong winds within that TW.
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Quoting canesrule1:
this blob right now is not even predicted by the NHC for development in the next 48 hours so until the NHC goes yellow with this AOI it is just a wave nothing more or less.


Its got a yellow circle around it. What are you talking about?
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Thanks Dr.........Status Quo for now as we head into mid-August shortly...
Member Since: August 8, 2006 Posts: 0 Comments: 9122
Fleet NAV/PAC message details OKINAWA bracing for TYPHOON Condition as the Typhoon approaches..

Discussion..
3. Forecast reasoning.
A. The forecast reasoning has not significantly changed since
the last prognostic reasoning bulletin.
B. Ts 09w will continue to track westward along the southern
periphery of the str located to the northeast. Environmental
analysis indicates that the system will remain in favorable sea
surface and vertical wind shear environments for the next 48 hours.
As the TUTT to the east tracks westward and closes the distance to
09w, outflow is expected to improve and intensification is expected.
There is the potential for rapid intensification over the next 24
hours as the system tracks over a pocket of warmer water and as the
TUTT to the east gets closer to 09w. Model guidance is in good
agreement with a tight grouping of most of the objective aids.
NOGAPS and GFS both track the system slightly more south and much
slower than the main group, possibly because they are initializing
the system as smaller and weaker than analyzed.
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I'm still sticking with my 11/5/3 Atlantic 19/11/5 Pacific forecast.
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12z 18h GFS
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12z GFS 12h
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Storm ID GMTime Lat Lon kts mbars
MORAKOT 09W Aug04,06:00 22.3 135.3 40 998
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Thanks...Dr. Masters!!
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Good Evening all
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Thank you Dr.Masters for the updates on TSR and CSU.
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Quoting canesrule1:
this blob right now is not even predicted by the NHC for development in the next 48 hours so until the NHC goes yellow with this AOI it is just a wave nothing more or less.


It is yellow on the NHC website.
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Quoting Dropsonde:
This should hopefully put an end to the dcasting proclamations that this disturbance is "losing organization"; it was never organized to begin with even when it looked circular. Satellites are deceptive.

The disturbance is probably going to look its worst in about three or four hours; it is around 1:30 (I think) where the disturbance is, and the easterly shear IS getting to it somewhat. We should expect it to look scrappy shortly. But as it moves out of the pocket of shear and into better conditions of about 15kt (and dropping, look at the tendency), I expect its appearance will improve as the atmosphere also begins to cool. Not coincidentally, that is when the blog's bipolar tendency will surface. :D



lol
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Nice "tropical" update, Doctor. Thanks.
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Quoting canesrule1:
so for right now i don't think this should be monitored.


What? NHC is now monitoring it, as they have put a yellow circle around it. Also, it remains to be seen what the track of this system, so shear, environment, etc. is still in question as the system goes west. All we should do is monitor the situation.
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Quoting VAbeachhurricanes:
i think Fujiwhara might happen.
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Quoting canesrule1:
this blob right now is not even predicted by the NHC for development in the next 48 hours so until the NHC goes yellow with this AOI it is just a wave nothing more or less.

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I do like that the NHC have added the first tagline on the main site now.
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This should hopefully put an end to the dcasting proclamations that this disturbance is "losing organization"; it was never organized to begin with even when it looked circular. Satellites are deceptive.

The disturbance is probably going to look its worst in about three or four hours; it is around 1:30 (I think) where the disturbance is, and the easterly shear IS getting to it somewhat. We should expect it to look scrappy shortly. But as it moves out of the pocket of shear and into better conditions of about 15kt (and dropping, look at the tendency), I expect its appearance will improve as the atmosphere also begins to cool. Not coincidentally, that is when the blog's bipolar tendency will surface. :D
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My bad i didn't know it was yellow.
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Quoting canesrule1:
this blob right now is not even predicted by the NHC for development in the next 48 hours so until the NHC goes yellow with this AOI it is just a wave nothing more or less.
so for right now i don't think this should be monitored.
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Here's the high shear near the islands by Sunday/Monday j/k

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this blob right now is not even predicted by the NHC for development in the next 48 hours so until the NHC goes yellow with this AOI it is just a wave nothing more or less.
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Not too thick.

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Split Window - Met-8/GOES-West - Latest Available
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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.