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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Hurricane FELICIA is shown to reach CAT 3 but then slow to a tropical storm by the weekend when it approaches Hawaii. What would cause the storm to decrease? It seems there would be ample energy/warm water to feed Felicia.
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Hurricane FELICIA

Member Since: July 21, 2009 Posts: 0 Comments: 552
Typhoon MORAKOT

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1269. HadesGodWyvern (Mod)
ya China has had many flooding cyclones this year
Member Since: May 24, 2006 Posts: 50 Comments: 45302
1268. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Warning #15
TROPICAL STORM GONI (T0907)
15:00 PM JST August 5 2009
=========================================

Subject: Category One Typhoon Overland South China

At 6:00 AM UTC, Tropical Storm Goni (992 hPa) located at 21.9N 112.2E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The storm is reported as almost stationary

RMSC Dvorak Intensity: T2.5

Gale-force Winds
================
120 NM from the center

Forecast and Intensity
=========================
24 HRS: 21.7N 111.5E - Tropical Depression

---
heh pressure is falling again.. cyclone center is still near the coast
Member Since: May 24, 2006 Posts: 50 Comments: 45302
Quoting HadesGodWyvern:
FKPQ30 RJTD 050600
TC ADVISORY
DTG: 20090805/0600Z
TCAC: TOKYO
TC: MORAKOT
NR: 9
PSN: N2235 E13205
MOV: W 11KT
C: 970HPA
MAX WIND: 65KT
FCST PSN +6HR: 05/1200Z N2250 E13050
FCST MAX WIND +6HR: 70KT
FCST PSN +12HR: 05/1800Z N2310 E12925
FCST MAX WIND +12HR: 75KT
FCST PSN +18HR: 06/0000Z N2330 E12800
FCST MAX WIND +18HR: 80KT
FCST PSN +24HR: 06/0600Z N2350 E12635
FCST MAX WIND +24HR: 85KT

---
increasing in intensity every 6 hours..
Definitely intensifying steadily.....looking mean on satellite imagery
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Quoting HadesGodWyvern:
oh I don't know Claudette.. that "Severe Typhoon" sign (90kts 925 hPa) in the forecast is scary looking


Yeah looks dangerous. Hope will lose power near China coast. China doesnt need another catastrophe, they have a bad year with rain and flooding.
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1265. HadesGodWyvern (Mod)
Ryukyu Islands near Taiwan which is like Okinawa region
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Looks like the WannaBe Ana went POOF....not really that unexpected when embedded within the ITCZ! Still has some life tho as it moves West!
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1263. HadesGodWyvern (Mod)
FKPQ30 RJTD 050600
TC ADVISORY
DTG: 20090805/0600Z
TCAC: TOKYO
TC: MORAKOT
NR: 9
PSN: N2235 E13205
MOV: W 11KT
C: 970HPA
MAX WIND: 65KT
FCST PSN +6HR: 05/1200Z N2250 E13050
FCST MAX WIND +6HR: 70KT
FCST PSN +12HR: 05/1800Z N2310 E12925
FCST MAX WIND +12HR: 75KT
FCST PSN +18HR: 06/0000Z N2330 E12800
FCST MAX WIND +18HR: 80KT
FCST PSN +24HR: 06/0600Z N2350 E12635
FCST MAX WIND +24HR: 85KT

---
increasing in intensity every 6 hours..
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HadesGodWyvern

which is the 1st islands to touch it for the typhoon?
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1261. HadesGodWyvern (Mod)
oh I don't know Claudette.. that "Severe Typhoon" sign (90kts 925 hPa) in the forecast is scary looking
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Last prediction of JMA was optimist.

i said 12-24 was a typhoon an it is, and who knows would be a Major, not too much chance but a little.

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1259. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Warning #17
TYPHOON MORAKOT (T0908)
15:00 PM JST August 5 2009
=========================================

Subject: Category Three Typhoon In Sea South of Japan

At 6:00 AM UTC, Typhoon Morakot (970 hPa) located at 22.6N 132.1E has 10 minute sustained winds of 65 knots with gusts of 95 knots. The typhoon is reported as west at 11 knots

RSMC Dvorak Intensity: T4.0

Storm-force Winds
==================
50 NM from the center

Gale-force Winds
================
325 NM from the center in the southern quadrant
240 NM from the center in the northern quadrant

Forecast and Intensity
=========================
24 HRS: 23.8N 126.6E - 85 knots (CAT 4/Typhoon)
48 HRS: 25.5N 122.8E - 90 knots (CAT 4/Typhoon)
72 HRS: 26.9N 118.9E - 55 knots (CAT 2/Severe Tropical Storm)
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MORAKOT is a Typhoon CAT1

TY 0908 (Morakot)
Issued at 06:50 UTC, 5 August 2009

Scale Large
Intensity Strong
Center position N22°35'(22.6°)
E132°05'(132.1°)
Direction and speed of movement W 20km/h(11kt)
Central pressure 970hPa
Maximum wind speed near the center 35m/s(65kt)
Maximum wind gust speed 50m/s(95kt)
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1257. code1
Understand. No satire now. I am seriously gonna try for a sandman visit now. Take care!
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Quoting code1:
I hear you KM, just making fun on a no sleep night!


lol, it's cool.

Hard to differentiate (at least for me) between satire and seriousness through text.
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1255. code1
I hear you KM, just making fun on a no sleep night!
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.
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1253. code1
Fish storm for EPAC and ATL this year! It's written in stone somewhere you know.
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1252. Drakoen
Felicia continues to track a little north of her forecast points.
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Does this wave stretch form 30w to 40w?
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What about 12N 32W?
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Freak91, Thanks,and believe me i definetly know the NHC knows what thier doing. I was confused about the 48 hours out, compared to what the mets are saying for possible low developement later this week.
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Quoting stormsurge39:
Why wouldnt the NHC keep the yellow cir up just for precaution? What ive been hearing and reading is that this wave would take a couple of days from now,if and when it developes. I know they have a reason, just dont understand.
Well, they have done very well with this wave as of yet. A yellow circle doesn't mean a wave will never turn into a storm; it simply means it won't in the next 48 hours. And I assure you that the wave we've all been watching will not be a tropical cyclone in the next 48 hours. Let the NHC do its thing.
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1246. Drakoen
Quoting Stormchaser2007:

Despite the lack of tropical activity...I think we can see somewhere near 9 storms.


I agree.
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1245. Drakoen
Quoting WeatherStudent:
But for how much longer, Drakoen?


Give it untill mid August. The HPC forecast for an upward MJO pulse lasting 2-3 weeks making note that we are overdue for a good MJO phase. During this period we could have consecutive cyclones forming as shear becomes more favorable in the MDR region in mid to late August.
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Quoting weatherwatcher12:

I expect we will hear the "0.0.0" thing again


I lol'ed at the 'government seeding' to dissipate tropical cyclones conspiracy someone put here. Got a hoot out of that.
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Quoting Claudette1234:
Felicia CAT2 hurricane good chance to be a Major

975mb 95mph gust 120mph


Its at 100mph.
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Felicia CAT2 hurricane good chance to be a Major

975mb 95mph gust 120mph
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Very nice tropical cyclone.

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Why wouldnt the NHC keep the yellow cir up just for precaution? What ive been hearing and reading is that this wave would take a couple of days from now,if and when it developes. I know they have a reason, just dont understand.
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Quoting CybrTeddy:
Ah well.. lotta bashing and arguing come sunrise.
with of course the '4 named or less' predictions. They've been doing that every time something doesn't develop.

Despite the lack of tropical activity...I think we can see somewhere near 9 storms.
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Quoting CybrTeddy:
Ah well.. lotta bashing and arguing come sunrise.
with of course the '4 named or less' predictions. They've been doing that every time something doesn't develop.

I expect we will hear the "0.0.0" thing again
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting Stormchaser2007:


This is an extremely weak tropical wave...Im not trying to downcast anything but it is more than likely that nothing will change between now and 8am.

Probably
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Ah well.. lotta bashing and arguing come sunrise.
with of course the '4 named or less' predictions. They've been doing that every time something doesn't develop.
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Quoting weatherwatcher12:


I know...but things in the tropics seem to change quickly when everybody goes to sleep


This is an extremely weak tropical wave...Im not trying to downcast anything but it is more than likely that nothing will change between now and 8am.
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Quoting Stormchaser2007:


There are no signs of it forming new convection... DMAX is in about an hour so it better get going soon or it will dissipate tomorrow. A circulation cannot sustain itself without convection...simple.


I know...but things in the tropics seem to change quickly when everybody goes to sleep
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1231. Drakoen
All is quiet in the Atlantic Basin
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Quoting weatherwatcher12:
It very well could fire back before morning like some other systems when they were deactivated.


There are no signs of it forming new convection... DMAX is in about an hour or so. It better get going soon or it will dissipate tomorrow or tomorrow night. A circulation cannot sustain itself without convection...simple.
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Quoting BurnedAfterPosting:


deactivated? it was never activated lol

I meant the circle lol
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1228. Fshhead
Mmmmm yellow circle go poof? LOL
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Quoting BurnedAfterPosting:


why?

Everyone will trade I told you so's then another group will come saying it still has a chance.
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Quoting weatherwatcher12:

It has good vorticity and IMO I agree that it needs some convection to organize further.


Wave has lost a lot of power, but still is there so the future is not clear.
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Quoting weatherwatcher12:
It very well could fire back before morning like some other systems when they were deactivated.


deactivated? it was never activated lol
It very well could fire back before morning like some other systems when they were deactivated.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:

In the morning there will be some uproar.


why?
Yeah,I'm beginning to think this wave aint gonna develop into anything. I'd be surprised if we got development by mid-August.
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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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