Less active Atlantic hurricane season foreseen by new model

By: Dr. Jeff Masters , 1:33 PM GMT on June 20, 2007

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A major new player in the seasonal Atlantic hurricane season forecast game is here--the UK Met Office, which issued its first Atlantic hurricane season forecast yesterday. The UK Met Office is the United Kingdom's version of our National Weather Service. Their 2007 Atlantic hurricane season forecast calls for ten named storms for the remainder of the season--12 for the entire season, when one includes Andrea and Barry. They make no forecasts for number of hurricanes or intense hurricanes, nor where the storms may strike. The UK Met Office forecast of ten storms for July through November is below the average of 12.4 for the active hurricane period that began in 1995, and well below the predictions of the other major seasonal forecast teams.

July-November 2007 Atlantic hurricane season forecasts (adjusted for the occurrence of Tropical Storms Andrea and Barry, where appropriate):

UK Met Office (June 19): 10 named storms.

Colorado State University (CSU) Phil Klotzbach/Dr. Bill Gray forecast (May 31): 16 named storms.

NOAA's forecast (May 22): 11-15 named storms.

Tropical Storm Risk, Inc. (TSR) forecast (June 4): 14.7 named storms.

How reliable are the UK Met Office forecasts?
This is the first year that the UK Met Office has issued a forecast of hurricane season activity, so we don't have any previous years to evaluate their forecasts. The results of their experimental forecasts issued for the 1987-2002 seasons are scheduled to be published later this year in the peer-reviewed journal Geophysical Research Letters. The UK Met Office claims that their forecast out-performed the forecasts made for the 2005 and 2006 Atlantic hurricane season issued by the other major seasonal forecast groups. I have high hopes for the UK Met Office forecast, since it is based on a promising new method--running a dynamical seasonal prediction computer model of the global atmosphere-ocean system. The Dr. Bill Gray/CSU forecast is based on statistical patterns of hurricane activity observed from past years. These statistical techniques do not work very well when the atmosphere behaves in ways it has not behaved in the past. The UK Met Office forecast avoids this problem by using a global computer forecast model--the GloSea model (short for GLObal SEAsonal model). GloSea is based on the HadCM3 model--one of the leading climate models used to formulate the influential UN Intergovernmental Panel on Climate Change (IPCC) report. GloSea subdivides the atmosphere into a 3-dimensional grid 3.75° in longitude, 2.5° in latitude (277.5 km), and 19 levels in the vertical. This atmospheric model is coupled to an ocean model of even higher resolution. The initial state of the atmosphere and ocean as of June 1, 2007 were fed into the model, and the mathematical equations governing the motions of the atmosphere and ocean were solved at each grid point every few minutes, progressing out in time until the end of November (yes, this takes a colossal amount of computer power!) It's well-known that slight errors in specifying the initial state of the atmosphere can cause large errors in the forecast. This "sensitivity to initial conditions" is taken into account by making many model runs, each with a slight variation in the starting conditions which reflect the uncertainty in the initial state. This generates an "ensemble" of forecasts and the final forecast is created by analyzing all the member forecasts of this ensemble. Forty ensemble members were generated for this year's UK Met Office forecast. The researchers counted how many tropical storms formed during the six months the model ran to arrive at their forecast of ten named storms for the remainder of this hurricane season. Of course, the exact timing and location of these ten storms are bound to differ from what the model predicts, since one cannot make accurate forecasts of this nature so far in advance.

The grid used by GloSea is fine enough to see hurricanes form, but is too coarse to properly handle important features of these storms. This lack of resolution results in the model not generating the right number of storms. This discrepancy is corrected by looking back at time for the years 1987-2002, and coming up with correction factors (i.e., "fudge" factors) that give a reasonable forecast. This year's GloSea forecast shows a cooling trend in the tropical Atlantic sea surface temperature (SST) compared to what we've seen in recent years, and is a major reason why the UK Met Office forecast is so much lower than the other seasonal Atlantic forecasts. I believe that the GloSea model has high enough resolution to do as good a job as the other seasonal hurricane forecasts this year, but it's hard to make an informed judgment until their research results are published. The GloSea forecast is based on sound science, though, and does call into question whether or not the other seasonal forecasts are forecasting unrealistically high levels of hurricane activity in the Atlantic this year. I think that is probably the case, and a better forecast can be made by averaging together the four models into a consensus forecast. Consensus forecasts are difficult to beat, and the consensus of the CSU, NOAA, TSR, and UK Met Office forecasts yields a prediction of 13 more named storms this year, for a total of 15.

The future of seasonal hurricane forecasts
The future of seasonal hurricane forecasts using global dynamical computer models is bright. A group using the European Center for Medium Range Weather Forecasting (ECWMF) model is also experimenting with some promising techniques using that model. Models like the GloSea and ECMWF will only get better as increased computer power and better understanding of the atmosphere are incorporated, necessitating less use of "fudge" factors based on historical hurricane patterns. If human-caused climate change amplifies in coming decades, statistical seasonal hurricane forecasts like the CSU's may be limited in how much they can be improved, since the atmosphere may move into new patterns very unlike what we've seen in the past 100 years. It is my expectation that ten years from now, seasonal hurricane forecasts based on global computer models such as the UK Met Office's GloSea will regularly out-perform the statistical forecasts issued by CSU.

Bill Proenza to appear on Thursday's Barometer Bob show
Thursday night June 21, new NHC director Bill Proenza will be the guest on the Barometer Bob Show. You can listen at barometerbobshow.com, or dial in via their toll-free number 1-866-931-8437 (1-866-WE1THER). If you want to ask him a question, you can do so using their Storm Chat web page.

Tropical Outlook
A cold front pushing off the East Coast of the U.S. on Thursday could trigger formation of a tropical depression by Friday or Saturday over the Gulf Stream waters between Daytona Beach, Florida and Cape Hatteras, North Carolina. Several of the computer models are forecasting that a weak low pressure system will form by Friday in this region. However, there will be a lot a wind shear close by, which may make any storm storm that does form subtropical or non-tropical. It is uncertain where such a storm might move, since steering currents will be weak. I'll have an update on this situation by Friday at the latest.

Jeff Masters

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1139. Jedkins
3:00 PM GMT on June 22, 2007
Posted By: weathersp at 2:08 PM GMT on June 22, 2007.

Ahh HA!! Storm Spotter Report of 7" of Rain... So at least its somewhat right.

06/22/2007 0537 am

4 miles se of Blandinsville, McDonough County.

Heavy rain m6.73 inches, reported by trained spotter.

Storm total since last evening.



Alrighty ya got me dangit lol.
1138. IKE
2:58 PM GMT on June 22, 2007
New Blog
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1137. weathersp
2:43 PM GMT on June 22, 2007
I highly doubt the NHC will call it an invest only because there was some flare up over the COC. I do believe if the blob can maintain itself for at least 6-10 hrs or so overnight then we will have 95L by tomrrow morning. If it can't do that then this blob is a dud.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1136. IKE
2:41 PM GMT on June 22, 2007
Posted By: moonlightcowboy at 9:39 AM CDT on June 22, 2007.
We'll get 95L close to Isla Mujeres, maybe before then...no supporting data, sorry, just a hunch.

...and thanks, Ike for reminding Whirlwind and the board that we don't want ANY roofs damaged!!!


You're welcome.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1135. moonlightcowboy
2:39 PM GMT on June 22, 2007
We'll get 95L close to Isla Mujeres, maybe before then...no supporting data, sorry, just a hunch.

...and thanks, Ike for reminding Whirlwind and the board that we don't want ANY roofs damaged!!!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1134. nash28
2:36 PM GMT on June 22, 2007
The key is it needs to maintain convection during the overnight hours. It did not do that last night.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1133. IKE
2:35 PM GMT on June 22, 2007
Posted By: whirlwind at 9:28 AM CDT on June 22, 2007.
ehh...what the heck. We are stressing ourselves out to bring life back into disturbances maybe just so they can become a cane. Its only June, plenty of possibilities happened. Its only gonna increase and increase. It will happen. And on that note... big one(s) will happen.


May there be no roofs damaged anywhere in the US this season.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1132. weathers4me
2:35 PM GMT on June 22, 2007
It's gonna fire as soon as the heating of the day starts to feed it. All it needs is some life. After that, it's in a pretty good environment thereafter. No land, just warm H2O. I don't think the shear forecast will be as high as predicted either.
Member Since: May 24, 2007 Posts: 0 Comments: 118
1131. WeatherMSK
2:33 PM GMT on June 22, 2007
The shear on this blob does seem like it is making it struggle a little. However, one thing i do notice is the flare up of convection near the true mid-level circulation right off the coast. I think this convection needs to be watched. If it flares up alot today, i feel this thing becomes an invest this weekend. Another scenario i see possibly playing out is that this thing moves more north and possibly slight north and east. Of course at that point this thing would have to contend with Cuba's high mountains. I predict Florida could see some tropical moisture from this system.
Member Since: February 12, 2007 Posts: 0 Comments: 479
1130. nash28
2:29 PM GMT on June 22, 2007
Pressures seem to be holding steady.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1129. whirlwind
2:28 PM GMT on June 22, 2007
ehh...what the heck. We are stressing ourselves out to bring life back into disturbances maybe just so they can become a cane. Its only June, plenty of possibilities happened. Its only gonna increase and increase. It will happen. And on that note... big one(s) will happen.
1128. kmanislander
2:25 PM GMT on June 22, 2007
Nothing unusual at the surface just to the NE of the spin off Honduras

Member Since: August 19, 2006 Posts: 0 Comments: 15842
1126. PensacolaDoug
2:15 PM GMT on June 22, 2007
DEATH to the BLOBS! (Unless they go out to sea)
Member Since: July 25, 2006 Posts: 0 Comments: 575
1125. kmanislander
2:12 PM GMT on June 22, 2007
Anyone have the inside scoop on how long the GHCC site will likely be down ?. We could sure use a few close ups of that area N of Honduras
Member Since: August 19, 2006 Posts: 0 Comments: 15842
1124. saveabeagle
2:12 PM GMT on June 22, 2007
My Daughter lives in North English, Ia 7.2 inches in her rain gauge
1123. whirlwind
2:11 PM GMT on June 22, 2007
The carrib disturbance is starting to refire. Circ is now no longer inland. That area as well as the gulf have very low shear. Perfect place for it to go and reintensify. Funny how these 'blobs' like to follow tracks similarly to Wilma.
1122. weathersp
2:08 PM GMT on June 22, 2007
Ahh HA!! Storm Spotter Report of 7" of Rain... So at least its somewhat right.

06/22/2007 0537 am

4 miles se of Blandinsville, McDonough County.

Heavy rain m6.73 inches, reported by trained spotter.

Storm total since last evening.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1121. weathers4me
2:00 PM GMT on June 22, 2007
As far as future steering currents. It is too early to predict exactly where the blob will go. The high can be eroded somewhat by 48h. Could go anywhere from TX to S FL. Just my thoughts
Member Since: May 24, 2007 Posts: 0 Comments: 118
1120. nash28
2:00 PM GMT on June 22, 2007
You're welcome StormW. Great analysis.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1118. kmanislander
1:55 PM GMT on June 22, 2007
Good morning all

Convection with the Caribbean disturbance is refiring just to the E of Roatan island. The Quikscat pass this morning does not show a surface low but there are a few wind barbs just off the N coast of Honduras that show a wind shift from SSE to ENE. Since there is a rotation that is quite evident in the sat images in the same area it could be that the rotation is all in the mid to upper levels or that the low was inland at the time of the pass and was just emerging at that time. It is possible that the barbs showing the wind shift were from the very N edge of a surface circulation that was emerging when the sat passed over. We will have to watch this area to see how things unfold throughout the day

Member Since: August 19, 2006 Posts: 0 Comments: 15842
1117. cchsweatherman
1:49 PM GMT on June 22, 2007
On the latest IR, it does in fact appear that convection is firing up on the southeast side of the "circulation". Now that it is over the warm Caribbean waters, it bares watching for possible tropical development.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
1116. Jedkins
1:37 PM GMT on June 22, 2007
Yep I figured that was off, even still, NWS says they have had 3 to 4 inches, and in the amount of time this fell in IOWA is really rough!


That area averages only about 20 inches of rain a year.


The weather is so weird this year, the pattern just will not go back to normal, its been way off course ever since 2007 started!
1115. TexasRiverRat
1:35 PM GMT on June 22, 2007
I do not see Carribean blob heading near Fla due to High in Gulf should track around right into Tex/LA
1111. weathersp
12:59 PM GMT on June 22, 2007
A lot of rain has fallen over the Quad Cities area last night.. Some places have gotten over 10" of rain.

wow
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1110. moonlightcowboy
12:57 PM GMT on June 22, 2007
GR8 post, SJ! They get no pay and their jobs are thankless usually...time spent away from family, and obviously in dangerous situations, too. They deserve recognition and our support! -- And, with that I have to add God Bless our troops, too!

....and uuummmm, good TGIF morning all!!! IMVHO, still think we'll get 95L later today! Headed to the GOM!!!

SJ, what's your take on the Caribbean blob?
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1109. watchingnva
12:49 PM GMT on June 22, 2007
thankfully no...lol...funny...

the car blob looks sick this morning. But, the circulation involved with it did in fact go inland overnight...it has now re-emerged off the nothern coast...and in the last few frames you can see convection trying to refire right near it. I have a feeling that by the afternoon it will be looking pretty good again...thing now is..it is moving directly for the gulf...no more land...we will see.

Photo Sharing and Video Hosting at Photobucket

I probably wont be able to check in till late this evening as my sister is having her first child today...so Ill probly be with family most of the day. You guys have a good one and Ill catch you later.

Chris.
Member Since: September 7, 2005 Posts: 7 Comments: 1516
1108. StormJunkie
12:44 PM GMT on June 22, 2007
Streaming video of memorial service can be found here.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1107. FormerFloridian
12:38 PM GMT on June 22, 2007
Posted By: emagirl at 12:36 PM GMT on June 22, 2007.
good morning everyone.......so do we still think the "blob" is going to develop


thankfully, no.
1106. nash28
12:37 PM GMT on June 22, 2007
Pretty much a crapshoot for the Caribbean blob.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1105. TheCaneWhisperer
12:37 PM GMT on June 22, 2007
Morning All!

Ship 4 is on the east side of the Caribbean disturbance. Pressure is rising, probably in relation to the lack of convection but, winds are 24kts 60 degrees. ENE
1104. StormJunkie
12:36 PM GMT on June 22, 2007
Memorial service for fire fighters this morning.
♥ Thanks to all our first responders!
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1103. emagirl
12:36 PM GMT on June 22, 2007
good morning everyone.......so do we still think the "blob" is going to develop
1102. nash28
12:33 PM GMT on June 22, 2007
Hoping the Caribbean disturbance can regain some life today.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1101. StormJunkie
12:29 PM GMT on June 22, 2007
neurian, you can find a bunch of great links on one page found here.

Member Since: August 17, 2005 Posts: 26 Comments: 16874
1100. Neurian
12:25 PM GMT on June 22, 2007
Thank You StormW
1097. nash28
12:06 PM GMT on June 22, 2007
Morning StormW, Pat.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1096. Neurian
12:02 PM GMT on June 22, 2007
I've been using this site for a year or so I dont see what you mentioned as a choice. "Experimental forecast Tropical Cyclone Genesis Potential Fields". What is the best site and selection to use when running models? Sorry to be difficult!
1093. Patrap
11:59 AM GMT on June 22, 2007
Hey StormW.The Friday arrives.
Member Since: July 3, 2005 Posts: 426 Comments: 128677
1091. Neurian
11:57 AM GMT on June 22, 2007
When everyone is looking at the model runs, are you selecting sea level pressures run or something else?
1089. Patrap
11:51 AM GMT on June 22, 2007
WAVEtrak split window...Link
Member Since: July 3, 2005 Posts: 426 Comments: 128677

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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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