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 AllStar17:


IKE, what area are you taking about? The area with high vorticity near 30W?


The more I look at it Ike.....the thunderstorms and the highest vorticity are fairly close to each other. This might night be done yet. The easterly shear must be lessening.....this may stand a chance after all.
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Quoting AllStar17:


IKE, what area are you taking about? The area with high vorticity near 30W?


I guess thats where he is referring too.....That means the AOI has not moved for 3 days.....
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Yeah, ECMWF isn't showing anything thru 8/15...hmmm...

Link
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1419. amd
Quoting AllStar17:


Dean was a major hurricane without an eye, I think.


a clear eye is a sign of a strong hurricane, but the two are not correlated. A hurricane can be extremely strong, but not have a clear eye. The best example is hurricane opal in 1995.

Opal peaked out with winds of 150 mph, pressures below 920 mb, but did not have a clear eye, although it obviously had an eye, just not a cloud free eye.

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Quoting IKE:
AOI w/a nice vort...moving into lower shear soon....



IKE, what area are you taking about? The area with high vorticity near 30W?
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Quoting Thundercloud01221991:


I understand that but right now it does not even have a perfectly round eye with a warm center


Dean was a major hurricane without a clear eye, I think.
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Good Morning.....Did not have a chance to check in last evening but the wave seems to have lost it's mojo overnight....With all of the current activity in the Pacific Basin (4 storms), I think that things will pick up in the Atlantic when the Pacific activity dies down as is often the case and that may still be a few weeks away (somewhere around the "traditional" August 14th average for August starting first storms).....In the meantime, hot and sunny around the Gulf States.
Member Since: August 8, 2006 Posts: 0 Comments: 8822
"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."

They increased their forecast? Really? They sure are putting a lot of faith in (potentially) higher SSTs.
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1412. hahaguy
Just looked at our aoi and it's not looking to good. But we shall see if it can get it's act together or not.
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1411. IKE
AOI w/a nice vort...moving into lower shear soon....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
1409. msphar
Looks like Felicia dies between 140W and 150W. Big island will see 'nuthin' but a few gusts above ambient winds.
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Quoting Claudette1234:

MJFELICIA.100kts-960mb-137N-1283W
TYMORAKOT.60kts-978mb-230N-1309E
TSENRIQUE.45kts-1000mb-169N-1215W
GONI.20kts-1007mb-220N-1121E


You were mentioning earlier issues with flooding in China.
HK Observatory 256K radar loop
In the HK Observatory 256Km radar loop you can clearly see TS Goni spinning away stationary just up the coast. Talk about your training t-storms. Folks on the side of the storm where it's dragging in moisture off the South China Sea must be getting some nasty amounts of rain.
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1407. msphar
Love the puppet.
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1406. SQUAWK
Quoting Squid28:
Okay, I googled this before I asked on here but really can not find a good answer.....

what is the cause/why does the quickScat "miss" areas during a pass every so often? I know rain can contaminate the readings, but what I am talking about is when you will see the graphic and it is just devoid of any data for a large swath of area.


OK, here is the best I can give you. The satellite is in a polar orbit. As it orbits, the earth is spinning. With the limited scan width of the satellite, it cannot cover enough of the earth on each pass to give contiguous data, so it misses a swath on each pass. That is why there are blank areas between passes.
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1405. Walshy
My prediction for "09.

7-2-1

August storms = 2
September storms = 4
Other = 1

*Error can be within 5*
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MJFELICIA.100kts-960mb-137N-1283W
TYMORAKOT.60kts-978mb-230N-1309E
TSENRIQUE.45kts-1000mb-169N-1215W
GONI.20kts-1007mb-220N-1121E
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Quoting AllStar17:


The NM of the eye does not matter in regards to the category, strength of the storm.

True but the Dreaded Pin Hole eye has a
significant intimidation factor, Why, its a pin hole eye!
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Quoting AllStar17:


The NM of the eye does not matter in regards to the category, strength of the storm.


I understand that but right now it does not even have a perfectly round eye with a warm center
Member Since: August 1, 2006 Posts: 28 Comments: 3716
Quoting Thundercloud01221991:
I do not think Felicia will get to Cat 4 till we get a clear eye around 20-40 NM wide


The NM of the eye does not matter in regards to the category, strength of the storm.
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Quoting weatherwatcher12:

I expect we will hear the "0.0.0" thing again


Yup, that'll probably come from Ike, first thing tomorrow morning, you'll see.

0-0-0 Well no

But my original forecast from early June is starting to look pretty good.
5-2-0 First named storm Sept 2
Five named storms
Two Hurricanes
zero Major

Crow Stew, I prefer PIE, but not just yet!
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Good morning.

Looks like our AOI is weakening. It has fired some convection and still has some circulation (albeit weak). Felicia is still intensifying. It would not surprise me if she got to Cat. 4 before leveling off.
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1397. Patrap
WP092009 - Tropical Storm MORAKOT
RAAMB page




Enhanced Infrared (IR) Imagery (4 km Mercator)



Storm Relative 1km Geostationary Visible Imagery
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1396. cg2916
Let's get talking about the AOI in the Atlantic or Felicia.
Member Since: December 21, 2007 Posts: 13 Comments: 3032
Quoting Squid28:
Okay, I googled this before I asked on here but really can not find a good answer.....

what is the cause/why does the quickScat "miss" areas during a pass every so often? I know rain can contaminate the readings, but what I am talking about is when you will see the graphic and it is just devoid of any data for a large swath of area.


The bird is bent.. they need a new one.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
I do not think Felicia will get to Cat 4 till we get a clear eye around 20-40 NM wide
Member Since: August 1, 2006 Posts: 28 Comments: 3716
Quoting Patrap:
Have MRI at 10:30 CDT, so Im Java Less.


Good luck Pat - hope everything goes well.
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1391. Patrap
Thanks Chief,cg2916,hurricanehanna..lil Bulging disc in the ol L5.

Get to go to a Civillian MRI Suite for it,fancy smancy,LOL
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1390. cg2916
Quoting Patrap:
Have MRI at 10:30 CDT, so Im Java Less.

Good luck. Maybe you'll get java afterwards.
Member Since: December 21, 2007 Posts: 13 Comments: 3032
1389. cg2916
Quoting IKE:
Good morning to all.

82 degrees outside and sunny.

Good morning IKE, I'm 80 and sunny, maybe a little rain later.
Member Since: December 21, 2007 Posts: 13 Comments: 3032
1388. Squid28
Okay, I googled this before I asked on here but really can not find a good answer.....

what is the cause/why does the quickScat "miss" areas during a pass every so often? I know rain can contaminate the readings, but what I am talking about is when you will see the graphic and it is just devoid of any data for a large swath of area.
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1387. msphar
Is Pat still doing the 'Nuthin' puppet or did he get bored and drifted away ?
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Good morning ike

Major Felicia seems stronger and stronger, do you think can get CAT4 ?
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1384. cg2916
Hey, everyone. Looks like we got an AOI out there.
Member Since: December 21, 2007 Posts: 13 Comments: 3032
1383. IKE
Good morning to all.

82 degrees outside and sunny.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Morning all...had a few minutes this morning to check in on things. Haven't had much time this summer for learning on here - I miss it! I see the yellow circle/AOI is gone, but are conditions favorable for it to be of interest again?
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1381. Patrap
Have MRI at 10:30 CDT, so Im Java Less.
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Quoting StormW:
Good morning Pat, Ike, Tim and all!


Hi StormW
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1378. Patrap
Up and atum Chief..morning,

Got java?

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1376. Patrap
G'morning Ike,everyone

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TAMPA time will tell
Member Since: August 22, 2006 Posts: 0 Comments: 2617
yellow circle a distinct possibility
Member Since: August 22, 2006 Posts: 0 Comments: 2617
Quoting stoormfury:
convection is on the increase. low level clouds are streaming to the area of low pressure, indicative of good low level convergence. the increasing 850mb vortcity is also indicative of a system trying to organise


JUst looked at all the items you described.....none of that is accurate....sorry!
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1372. IKE
Looks like that AOI is moving almost due west.

Yellow circle?
Member Since: June 9, 2005 Posts: 23 Comments: 37858

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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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