A 65% chance of an above-average 2008 hurricane season : NOAA

By: Dr. Jeff Masters , 6:25 PM GMT on May 22, 2008

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There is a 65% chance that year's Atlantic hurricane season will have above average activity, and only a 10% chance it will be below average, according to today's seasonal hurricane forecast issued by the National Oceanic and Atmospheric Administration (NOAA). In an effort to emphasize the uncertainties in their forecast, NOAA for the first time included a probability with their "numbers" forecast. The numbers NOAA predicts are 12-16 named storms, 6-9 hurricanes, 2-5 intense hurricanes, and an Accumulated Cyclone Energy (ACE) index 100%-210% of the median. They put the odds of experiencing those numbers at 60-70%. This probability is based on the numbers seen in past hurricane seasons that had May climate patterns similar to those of 2008. An average hurricane season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecasters also call for a 70% chance of a below normal season in the eastern Pacific off the coast of Mexico, and a below normal season in the Central Pacific near Hawaii.

The forecasters considered two main climate signals to make their forecast:

1) Continuation of conditions that have been conducive to above-normal Atlantic hurricane activity since 1995, including above-average sea-surface temperatures in the eastern tropical Atlantic Ocean (Figure 1). Between 1995-2007, the Atlantic has averaged 14.5 named storms, 8 hurricanes, and 4 major hurricanes, with an average ACE index of 167% of the median. NOAA classifies nine of the thirteen seasons since 1995 as above normal, with seven being hyperactive (ACE > 175% of median). Only four seasons since 1995 have not been above normal. These include the three El Niño years (1997, 2002, and 2006) and the 2007 season.

2) La Niña or neutral conditions during the peak months (August-October) of hurricane season. The current weak La Niña episode has substantially weakened the upper-level west-to-east winds over the tropical Atlantic. These winds create much of the wind shear that inhibits hurricane development. La Niña is expected to persist (or weaken slightly to neutral) by hurricane season, and these weak westerly winds are predicted to persist over the Atlantic, bringing low levels of wind shear.



Figure 1. SST image from NOAA's May 22, 2008 seasonal hurricane forecast.

Where will this year's storms hit?
NOAA does not present any forecasts of where the steering currents might take this year's hurricanes. In general, steering currents are not predictable more than 5-7 days in advance, although sometimes one can stretch this to two weeks. As far as U.S. landfalls go, I believe that the climatology of landfalls since 1995 offers the best forecast. Between 1995-2007, the U.S. experienced an average of 4.7 named storms making landfall, of which 1.9 were hurricanes and 0.8 were intense hurricanes.

How believable is the NOAA forecast?
Mathematical analysis of forecasts made in late May and early June by two groups--Tropical Storm Risk Inc., and the Colorado State University group led by Phil Klotzbach and Dr. Bill Gray--have shown that these forecasts had reasonable skill over the past decade or so. Unfortunately, NOAA has never performed a mathematical analysis of their May forecasts, so we don't know whether their forecasts have any skill. Their forecast did poorly last year, and the head of NOAA's forecast team, Dr. Gerry Bell, provides an interesting analysis of why last year's forecast failed.

Commentary
NOAA's forecast is a reasonable one--but then, since 1995, it's always been smart to forecast an above-average hurricane season, barring an obvious El Niño event. I like that NOAA is looking to insert more uncertainty into their forecast by providing a percent chance of their expected numbers to verify. However, they really need to provide some verification numbers of how much skill these forecasts have, if they want to make them more useful. In addition, they should consider dropping the "numbers" forecast of named storms, since the number of named storms often does not give a true picture of how active a hurricane season is. For example, recall the 15 named storms from 2007, which was about 50% above average! Yet the ACE index, a more true measure of the destructive power of the storms, was 31% below average. ACE index is a better measure because it uses the square of each storm's peak winds, summed up over the lifetime of the storm. Wind damage from a hurricane is proportional to the square (and possible the cube) of the peak winds, and total damage increases by a factor of 5-10 for each Saffir-Simpson Category between Cat 1 and Cat 4. According to Pielke and Landsea (1998), a doubling of wind speed--from a 74 mph Category 1 hurricane to a 148 mph Category 4 hurricane--has historically resulted in 250 times more damage for U.S. landfalling hurricanes. This figure includes storm surge, flooding, and wind damage.

The Colorado State University group led by Phil Klotzbach and Dr. Bill Gray issues their seasonal hurricane forecast on June 3 this year, and I'll be sure to provide additional commentary then.

Jeff Masters

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576. BahaHurican
12:27 PM GMT on May 24, 2008
Morning all.

Unfortunately, all that lovely precipitation missed my part of the Bahamas . . . But I admit I wasn't expecting anything until next week. Perhaps the GFS forecast people have been talking about will pan out in that it may bring some tropical rain to the area . . .
Member Since: October 25, 2005 Posts: 19 Comments: 22322
575. TampaSpin
2:26 PM GMT on May 23, 2008
It appears that a trough has a low that is getting alittle better organized in the GOM. Some great rain could be coming to the SE regions.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
574. TampaSpin
2:23 PM GMT on May 23, 2008
This has alittle spin going maybe some good rain coming to florida.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
573. KrazyKaneLove
1:38 PM GMT on May 23, 2008
g'morning everyone, looks like we will soon start seeing some activity..also (head's up) my mom is visiting florida in 3 weeks, last time she came down from Kansas City to visit, she brought her friend Wilma with her..lol, Charlie came with her the previous trip..so beware, she just might be a better cane predictor than NOAA.
Member Since: September 7, 2007 Posts: 0 Comments: 429
572. CJ5
1:32 PM GMT on May 23, 2008
I appears there is a potential 90L at 27, as you guys have been commenting on. Things are begining to take shape for the 08 season.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
571. TerraNova
1:24 PM GMT on May 23, 2008
Anything new and exciting I should know about?

Morning! There's a wave with a low level spin the Eastern Atlantic but thats really not looking like anything special in terms of development. The GFS is still up to it's SW Caribbean storm.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
570. FLWeatherFreak91
1:23 PM GMT on May 23, 2008
569. smmcdavid 9:19 AM EDT on May 23, 2008 Hide this comment.
Good morning all...

Anything new and exciting I should know about?


There is a well-defined tropical wave approaching the central atl and the GFS is still forming a system in the SW carib and moving into the gulf later next week.
Member Since: December 1, 2006 Posts: 2 Comments: 3625
569. smmcdavid
1:19 PM GMT on May 23, 2008
Good morning all...

Anything new and exciting I should know about?
Member Since: September 20, 2005 Posts: 31 Comments: 2309
568. TerraNova
1:11 PM GMT on May 23, 2008
does anybody think that they will name it an invest?(the tropical wave)

It's possible; but it will need to sustain itself for most of today and into tomorrow before they start thinking of declaring 90L. I'd like to see it sustain itself and look at what the 12z model runs have to say about this before I make my opinion...satellite presentation is fairly impressive and there is obviously a LLC in the making. Dry air will likely become a problem for this somewhere down the line.

It's not in a favorable position, either.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
567. Ivansrvivr
12:59 PM GMT on May 23, 2008
Gamma, Most of Palm Beach Co. got well over an inch. I got almost three. Local news claimed areas close by got more than 4. With the calmer winds, a weak seabreeze and the likely interaction those will have with the mid level system over N Florida, today and tomorrow are the best bets for rain we have had in months. Yesterdays rains will help fuel todays storms too.
566. 69Viking
12:55 PM GMT on May 23, 2008
Good morning everyone! TGIF! The rain missed my portion of the panhandle too.
Member Since: August 25, 2006 Posts: 1 Comments: 3055
565. NEwxguy
12:52 PM GMT on May 23, 2008
GM, all,those videos from colorado were pretty intense. People out in that area,will have to watch the skies again today,atomosphere is primed.
Member Since: September 6, 2007 Posts: 881 Comments: 15840
564. hurricane10
12:52 PM GMT on May 23, 2008
does anybody think that they will name it an invest?(the tropical wave)
563. seflagamma
12:44 PM GMT on May 23, 2008
good morning my friends! Happy Friday to you. I see we have stuff to watch out there already. Always love it when it becomes interesting.

Man, when I got home last night noticed the streets wet and some water on the grass, etc... I just knew we got a little rain out of those storms that crossed South Fla yesterday but my rainguage was empty! Nothing measurable fell at my house. Bah! But some areas got as much as an inch of rain yesterday all around me.. it was sort of "hit or miss" type of storms...
hope we have better luck today! LOL
Member Since: August 29, 2005 Posts: 299 Comments: 40917
562. ClearH2OFla
12:40 PM GMT on May 23, 2008
see you all later got to get ready.
561. ClearH2OFla
12:39 PM GMT on May 23, 2008
NOt much working 10-500 today. Gonna be kinda boring my girl fly to Jersey so no fun at work.
560. stoormfury
12:38 PM GMT on May 23, 2008
W/V image of eastern ATL



W/Vimage of eastern Link
Member Since: August 22, 2006 Posts: 0 Comments: 2713
558. ClearH2OFla
12:35 PM GMT on May 23, 2008
Hey StormW how goes it. How is your Father?
557. weathermanwannabe
12:35 PM GMT on May 23, 2008
Morning All....I see you guys are already on the ball in terms of the semi-closed wave in the eastern Altlantic.......For me, at home in the Tallahassee area today, I was awoken this early am to the sound of rain on skylight; Ahhhh, slept in a little bit and we have been getting some nice steady rain for the past several hours........The plants and lawn very happy this morning.............
Member Since: August 8, 2006 Posts: 0 Comments: 9234
554. Ivansrvivr
12:18 PM GMT on May 23, 2008
550, it all fell on the East Coast. Today and tomorrow look more favorable for both east and west coasts to get some rain.
553. moonlightcowboy
12:17 PM GMT on May 23, 2008
I hear ya, Ivan!

Photobucket
Member Since: July 9, 2006 Posts: 184 Comments: 29610
551. nash28
12:14 PM GMT on May 23, 2008
Morning all.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
549. Ivansrvivr
12:07 PM GMT on May 23, 2008
If it were July, that E.Atl system would be a real concern for down the road. It may well develop briefly but would then tend to recurve and SSTs would not support it long. If the E ATL stays as active as it has been it will likely be a busy season.
548. moonlightcowboy
12:01 PM GMT on May 23, 2008
StormW, if the wave at 27w continues to run low as it is now, couldn't it slip in under the TUTT (looks to lifting out to the ne) as it moves west?
Member Since: July 9, 2006 Posts: 184 Comments: 29610
546. TerraNova
11:41 AM GMT on May 23, 2008
Morning StormW! What's your opinion concerning the GFS storm as well as the low level circulation out in the east?
Member Since: July 30, 2007 Posts: 76 Comments: 4063
544. Ivansrvivr
11:38 AM GMT on May 23, 2008
MLC, Casper is running for Mccain's soon to be vacated senate seat.
543. moonlightcowboy
11:38 AM GMT on May 23, 2008
Ivan, agreed.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
542. moonlightcowboy
11:36 AM GMT on May 23, 2008


Not really any dry air to speak of in the immediate wave area, but there is some further out near 39w according to wv.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
541. TerraNova
11:36 AM GMT on May 23, 2008
Finally...
CNN: Myanmar accepts aid
Member Since: July 30, 2007 Posts: 76 Comments: 4063
540. Ivansrvivr
11:35 AM GMT on May 23, 2008
537. Morning MLC. They just keep on coming off the coast of Africa dont they. If it were mid July, that would be one to watch. With the warming of the waters off the coast of Africa, those waves may not tend to dissipate as the peak of CV season hits. That would ultimately be a good thing as they would recurve very early.
539. StormJunkie
11:30 AM GMT on May 23, 2008
Morning all :~)

So, I see the GFS long range has gone form Tampa to the Tx/Mx border! lol, only a minor discrepancy!

Alright, off to work. See y'all in a little while.
Member Since: August 17, 2005 Posts: 26 Comments: 16872
538. Ivansrvivr
11:30 AM GMT on May 23, 2008
536. While you are correct, the models are all pointing toward E-Pac development. Climatology agrees. Once development begins in the E-Pac, outflow and sinking air surrounding any such system would affect the surrounding steering currents. I've seen too many early season times like this when the upper levels favor both the W.Caribbean and the E-Pac and the E-Pac wins this time of year almost every time. That is why the E-Pac season begins in Mid May and the Atlantic Season waits till June. If this were October and we were watching a similar situation I'd bet on the W.Caribbean but this is May.
537. moonlightcowboy
11:21 AM GMT on May 23, 2008


...appears to be building a cloud top, but will have to hold on at that latitude. The storm to the right, just coming off the coast looks nice, but will likey dissipate out over water.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
536. TerraNova
11:14 AM GMT on May 23, 2008
534. Don't know if this matters or not but 850mb - 700mb steering currents are pointing northward.

CIMSS Layer Mean Steering Analyses
Member Since: July 30, 2007 Posts: 76 Comments: 4063
535. Cavin Rawlins
11:14 AM GMT on May 23, 2008
My thoughts on Noaa's Outlook
The Tropics


Member Since: July 24, 2005 Posts: 407 Comments: 19076
534. Ivansrvivr
11:11 AM GMT on May 23, 2008
532.With the low in the W.Caribbean that far south, what is going to dig that far south and pull the low northward? That low will move slowly westward and emerge over the E-Pac or anything developing over the E-Pac will absorb it. What may end up being of more interest is the stationary front in the Florida Straights. If it sits and festers down there long enough, that could be a source of development.
533. stoormfury
11:06 AM GMT on May 23, 2008
recent QuickScat ot the area . surface winds are about 25knots





Link
Member Since: August 22, 2006 Posts: 0 Comments: 2713
532. TerraNova
11:05 AM GMT on May 23, 2008
I just noticed that the NAM has a low in the SW Caribbean at around 78 hours. However, I think the EPAC scenario is far more likely at this point, both due to proximity issues and model concensus.

Member Since: July 30, 2007 Posts: 76 Comments: 4063
531. Ivansrvivr
11:02 AM GMT on May 23, 2008
Development in the E-Pac usually sucks the life out of anything developing in the W-Caribbean. That is why although the upper atmosphere favors the W.Caribbean both early in the season and late in the season, development usually occurs in the W-Caribbean late in the season when the Pacific season is nearing it's end.

As for the GOMex blob, while it is marching east, the sun is rising over the peninsula which will become unstable very quickly. Look for storms to fire to the south of the current storms over N Florida and be spreading southward by mid-day. If you live on the eastern half of the peninsula, watch for some strong storms later today.
529. stoormfury
10:58 AM GMT on May 23, 2008
thanks to 456 the blog will be interesting today. the emphasis will shift from the gfs and the waestern carib to the far eastern atl. it is also puzzling how none of the models latched on to this system. it is rather early and against climatology to see development so far out in the atl.
Member Since: August 22, 2006 Posts: 0 Comments: 2713
528. TampaSpin
10:51 AM GMT on May 23, 2008
Member Since: September 2, 2007 Posts: 178 Comments: 20443
527. Chicklit
10:49 AM GMT on May 23, 2008
"The GOmex blob is marching east."

Hopefuly southeast.

Member Since: July 11, 2006 Posts: 14 Comments: 11353
526. TerraNova
10:48 AM GMT on May 23, 2008
Member Since: July 30, 2007 Posts: 76 Comments: 4063

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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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