Average hurricane season foreseen by CSU, NOAA, and TSR

By: Dr. Jeff Masters , 4:45 PM GMT on June 02, 2009

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A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued June 2 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 11 named storms, 5 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 88% 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 April forecast, which 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 (28% chance, 31% chance is average) and the Gulf Coast (28% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane.

The forecasters cited several reasons for an average season:

1) Sea surface temperature (SST) anomalies in the tropical Atlantic are quite cool. In fact, these SST anomalies are at their coolest level since July 1994. Cooler-than-normal waters provide less heat energy for developing hurricanes. In addition, an anomalously cool tropical Atlantic is typically associated with higher sea level pressure values and stronger-than-normal trade winds, indicating a more stable atmosphere with increased levels of vertical wind shear detrimental for hurricanes. Substantial cooling began in November 2008 (Figure 1), primarily due to a stronger than average Bermuda-Azores High that drove strong trade winds. These strong winds increased the mixing of cool waters to the surface from below, and caused increased evaporational cooling.

2) Hurricane activity in the Atlantic is lowest during El Niño years and highest during La Niña or neutral years. This occurs because El Niño conditions bring higher wind shear over the tropical Atlantic. The CSU team expects the current neutral conditions may transition to El Niño conditions (70% chance) by this year's hurricane season. I discussed the possibility of a El Niño conditions developing this year in a blog posted Friday.


Figure 1. Change in Sea Surface Temperature anomaly between November 2008 and 2009. Most of the Atlantic has cooled significantly, relative to normal, over the past 7 months. Image credit: NOAA/ESRL.

Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: neutral to slightly warm ENSO conditions, slightly below-average tropical Atlantic SSTs, and above-average far North Atlantic SSTs during April-May. Those five years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 2001, featuring Category 4 storms Michelle, which hit Cuba, and Iris, which hit Belize; 1965, which had Category 3 Betsy that hit New Orleans; 1960, which had two Category 5 hurricanes, Ethyl and Donna; and 1959, which had Category 3 Hurricane Gracie, which hit South Carolina. The mean activity for these five years was 10 named storms, 6 hurricanes, and 2 intense hurricanes, almost the same as the 2009 CSU forecast.

How accurate are the June forecasts?
The June forecasts by the CSU team have historically offered a skill of 20 - 30% higher than a "no-skill" forecast using climatology (Figure 2). This is a decent amount of skill for a seasonal forecast, and these June forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. This year's June forecast uses the same formula as last year's June forecast, which did quite well predicting the 2008 hurricane season (prediction: 15 named storms, 8 hurricanes, 4 intense hurricanes; observed: 16 named storms, 8 hurricanes, 5 intense hurricanes). An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.44 to 0.58 for their June forecasts, which is respectable.


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.

NOAA's 2009 hurricane season forecast
The National Oceanic and Atmospheric Administration (NOAA), issued its 2009 Atlantic hurricane season forecast on May 21. NOAA anticipates that an average season it most likely, giving a 50% chance of a near-normal season, 25% chance of an above-normal season, and a 25% chance of a below-normal season. They give a 70% chance that there will be 9 - 14 named storms, 4 - 7 hurricanes, 1 - 3 major hurricanes, and an Accumulated Cyclone Energy (ACE) in the 65% - 130% of normal range. The forecasters cited the following main factors that will influence the coming season:

1) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO).

2) There will either be an El Niño event or neutral conditions in the Equatorial Eastern Pacific. An El Niño event should act to reduce Atlantic hurricane activity. However, our skill at predicting an Niño in late May/early June is poor, so there is high uncertainty about how active the coming hurricane season will be.

3) Cooler-than-average SSTs are currently present in the eastern tropical Atlantic. These cool SSTs are forecast to persist through into August-September-October (ASO). ASO SSTs in the eastern tropical Atlantic have not been below average since 1997. Cooler SSTs in that region are typically associated with a reduction in Atlantic hurricane activity.

Thus, they expect that even though we are in an active hurricane period, the presence of an El Niño or cool SSTs in the eastern Atlantic could easily suppress activity, making a near-average season the most likely possibility. They note that two promising computer models, the NOAA CFS model and the European Center for Medium-Range Weather Forecasts (ECMWF) Global Climate Model System 3, both forecast the possibility of a below-average hurricane season.

2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) has joined the ranks of NOAA and Colorado State University in calling for near-average activity. The latest TSR forecast issued June 4 calls 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 close to the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes, and are sharp reduction from their April forecast of 15 named storms, 7.8 hurricanes, and 3.6 intense hurricanes. TSR predicts a 50% chance that this season will be in the bottom 1/3 of years historically, and a 40% chance that U.S. landfalling activity will be in the lowest 1/3 of years historically. TSR gives a 32% chance of a near-normal season, and a 17% chance of a below normal season. TSR rates their skill level as 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.2 named storms will hit the U.S., with 1.3 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 April forecasts for U.S. landfalls is 7 - 18% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 0.9 named storms, 0.4 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their reduced forecast: a large and unexpected cooling of sea surface temperatures in the tropical Atlantic, and warmer SSTs in the Equatorial Eastern Pacific (which might lead to an El Niño event that will bring high wind shear to the Atlantic). TSR expects faster than than normal trade winds from July - September over the Main Development Region (MDR) for hurricanes over the Atlantic (the region between 10° - 20° N from Central America to Africa, including all of the Caribbean). Trade winds are forecast to be 0.83 meters per second (about 1.7 mph) faster than average in this region, which would 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. TSR forecasts that SSTs will cool an additional 0.3°C compared to average over the MDR during hurricane season.

Air France crash
The Air France Flight 447 A330 aircraft that disappeared over the mid-Atlantic Ocean yesterday definitely crossed through a thunderstorm complex near the Equator, according to a detailed meteorological analysis by Tim Vasquez. He concludes that "the A330 would have been flying through significant turbulence and thunderstorm activity for about 75 miles (125 km), lasting about 12 minutes of flight time" but that "complexes identical to this one have probably been crossed hundreds of times over the years by other flights without serious incident". See also the excellent CIMSS satellite blog for more images and analysis of the weather during the flight.

Invest 92
NHC is tracking a storm near the Azores Islands (Invest 92L) that is probably the remnants of the core of an extratropical cyclone that closed off some warm air at the center. The system has developed some heavy thunderstorm activity near its center, making this a hybrid storm. However, with ocean temperatures near 62°F (16°C), this storm has little chance of becoming a named subtropical storm.

Jeff Masters

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406 & 407

You look for that kind of development when the low is forecast to stall or traverse the entire Gulf Stream like Andrea or TD 1, respectively.

The feature is expected to be a typical frontal system.

Also subtropical cyclones take a longer time to develop that true tropical cyclones.
Member Since: July 24, 2005 Posts: 407 Comments: 19076


This image is pretty much centered over this buoy. Showing continued trend to a westerly wind...There was also an anomalous temp rise just a short time ago. Unfortunately no pressure readings from this one. Any thoughts 456, HK, etc?
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you guys expecting the Big bend to get rain from this or just the western panhandle of FL. The rain we had been getting germinated bermuda seed that I wasn't expecting to do so, but the heat we have had in the last two days has wreaked havoc on the young plants.
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^ But right now I doubt the nhc will name it
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting HurricaneKing:


Latest NAM takes it off the georgia coast then off the carolinas in the gulf stream. I think if it stays offshore or onshore for a short time then a subtrop could form.


Agreed if it stays together relativly well on land it could develop in the atlantic
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting Weather456:
hurricaneseason2006;

Never give anything a 0% chance of development unless your 100% sure...lol

I've been montoring the area and shows little signs of amounting to much over the next 48 hrs. For one, there is no surface reflection suggesting much of the convection is being enhanced by upper level forces. Shear is forecast to decrease over the next day or two in a small region near the disturbance but this feature is expected to move shore in about 36 hrs and head NEward across the SE United States along a developing frontal boundary.



Latest NAM takes it off the georgia coast then off the carolinas in the gulf stream. I think if it stays offshore or onshore for a short time then a subtrop could form.
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The BLOB

that ate TEXAS

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Quoting Levi32:


And yet why do they let storms keep their names after they have been stripped bare of all clouds greater than 10 feet high?

The whole naming system is completely messed up.


Thank you!!!! I have a whole brainstorm in my head for over a year which i hope to get it down into an organized blog entry here SOON... tomorrow, next week... idk. Maybe people will actually view it and be like oh, nhc really IS f****d
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Dr Lyons just finished the tropical update, you could tell he was stunned by this system. Admitting there is a circulation, inflow and outflow and it was impressive. However he doubts it will develop further.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
hurricaneseason2006;

Never give anything a 0% chance of development unless your 100% sure...lol

I've been montoring the area and shows little signs of amounting to much over the next 48 hrs. For one, there is no surface reflection suggesting much of the convection is being enhanced by upper level forces (though some low level convergence maybe contributing). Shear is forecast to decrease over the next day or two in a small region near the disturbance but this feature is expected to move shore in about 36 hrs and head NEward across the SE United States along a developing frontal boundary.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting hurricaneseason2006:
It's not amazing, it's pathetic because some are looking for signs of development and ignoring 40 knots of vertical wind shear. =(


UHHH Barry formed like this in 40 knots of shear. The models are starting to show a Barry like storm forming from this mess thus it bears watching.
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400. beell
397-Hi!
We'll take it Ally! We're blobless here!
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Blobage S and Se of Here proper..ally.

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lol beell, that is why I went ahead and looked at it...and your recommendation...

Let's see how the GFS compares in about 45 minutes.
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Hey Pat, please keep the blob over there!...I don't want it at my house!..lol
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Quoting hurricaneseason2006:
It's amazing how some people look extra hard to find some evidence that the blob of convection in the Gulf is going to develop. I'm all for blob watching since the tropics are quiet but be objective rather than subjective.


Would you mind looking extra hard and finding some data that says it won't? Been waiting for some one to show me why it won't...So far the biggest negative is the shear; which is dropping, at least some.
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Terrebone Bay is Notorious for Meso Vortexs that migrate Ne..or east.
Even July Tstorms can gather mo and do weird stuff.


No one is expecting anything cept some rains and then a Frontal Passage Thursday.
Drier Air to Filter in Behind this Low,but Moisture returns for the Weekend.


GOM IR loop
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394. beell
Quoting StormJunkie:
Can not believe I am pointing this out, as I typically preach leaving the NAM in the closet for H season...but it shows a closed 1008mb low making landfall in Apalachicola at 54 hours...



Come out of the closet SJ-it does ok for stuff close to shores of NOAM and gives you another look.
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392. TX2FL
Good Evening,

I was wondering does anyone have the graphic or link to the "stoopid circle" that was posted last season? I want to show it to someone and I can't find it.
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We may be the only people paying attention to it, maybe the nhc sees it also. I know the TWC isn't paying attention, probably talking about gardening tips, or their failed Vortex 2 experiment. lol
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Sea, I was waiting for another reading or two to mention that...That said, that buoy showed a rise and fall in temp just a short time ago as well as a wind shift...


I am not ready for a limb yet, but it is an intriguing area...
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Agree.. wow.. nice vortex, patrap.

Again, great early season stuff.

One obs, but westerly at this buoy. First westerly I've seen in the gulf in quite some time.

Link
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Can not believe I am pointing this out, as I typically preach leaving the NAM in the closet for H season...but it shows a closed 1008mb low making landfall in Apalachicola at 54 hours...
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Ohhh is that roatation I see!!!
Member Since: May 27, 2009 Posts: 0 Comments: 4438
June 2 2009



*************************************************************************************


Hurricane Cindy July 5-6 2005
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384. beell
Quoting Chicklit:
Shear in Gulf still pretty high but dropping.


Dropping to about 40 knots...
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Shear in Gulf still pretty high but dropping.
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Link
Pretty lively in TX and north central GOM.
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With the last hour or so wind shift and the interesting temp readings at this buoy...Is it worth anything? Does not look to me like it is located where any sort of center could be?

Maybe Quickscat will get it after all...
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If you're still around CDL, agree on that wave out there. Something to keep an eye on.
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Quoting Chicklit:

Hey, is GulfScotsman in that picture?!


LOL..I bet some of us could be..Chicklit
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Quoting Patrap:
We need better Buoy Data...SJ

Who's for Mo Buoys with better Data ?







Here Here! Needed for sure !

Do a gap analysis and see for yourself :)

Link


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there's a low there,supposed to move west to east..
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More around 25/89 roughly. If anything, imo.

Seen the charts. Still thinking more E movement.

Great early season stuff. The large area of disturbed weather that 90L came out of was fascinating to me.

And here's another (albeit not as complex).
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Quoting Patrap:
We need better Buoy Data...SJ

Who's for Mo Buoys with better Data ?






Hey, is GulfScotsman in that picture?!
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18Z NAM & GFSO



Pretty spot on ..interesting.
Been watching that all day and evening.
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371. beell
The 00Z NAM may be worth a look on the Gulf activity. The 18Z was much better at showing a weak surface trough along 94W.
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Quoting Patrap:
This is crazy..but seems 09 will have a lot of er,stuff.

Current Slidell Radar Composite



I swear i see circulation in the thunderstorms
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I think,maybe..the Genesis Parent Low is way back here in the Sw to W GOM

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Thats the area I noticed in the GOM... IA1...LOL
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Hey BT..were gonna name the GOM AOI..got any suggestions?

I was thinking.."Almost 93L"

But its gaining character.
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This is crazy..but seems 09 will have a lot of er,stuff.

Current Slidell Radar Composite

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Hey bt, great to see ya.

imho...No
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Someone correct me if I am wrong, but if a center tried to form I would think it would be on the SW side of the convection no?
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WISHING EVERYONE A SAFE HURRICANE SEASON.
are they going to name that storm in the North Atlantic?
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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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