More pre-season predictions of a very active Atlantic hurricane season

By: Dr. Jeff Masters , 3:02 PM GMT on July 12, 2010

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Hello again, it's Jeff Masters back again after a week away. Well, the past week was a wicked hot time to be in New England, where I was vacationing, and I certainly didn't expect to see 98° temperatures in Maine like I experienced! Fortunately, it's not hard to find cold water to plunge into in New England. Thankfully, the tropics were relatively quiet during my week away, and remain so today. There are no threat areas in the Atlantic to discuss at present, and none of the reliable computer models is forecasting tropical cyclone development over the next seven days. The NOGAPS model does show a strong tropical disturbance developing near the waters offshore of Nicaragua and Honduras this weekend, though. With not much to discuss in the present-day tropics, let's take a look at more pre-season predictions of the coming Atlantic hurricane season.

2010 Atlantic hurricane season forecast from Penn State
Dr. Michael Mann and graduate student Michael Kozar of Penn State University (PSU) issued their 2010 Atlantic hurricane season forecast on May 28. Their forecast utilizes a statistical model to predict storm counts, based on historical activity. Their model is predicting 19 to 28 named storms in the Atlantic, with a best estimate of 23 storms. The forecast assumes that record warm SSTs will continue in the Atlantic Main Development Region for hurricanes. Dr. Mann has issued two previous forecasts, in 2007 and 2009. The 2007 forecast was perfect--15 storms were predicted, and 15 storms occurred. The 2009 forecast called for 11.5 named storms, and 9 occurred (the 2009 forecast also contained the caveat that if a strong El Niño event occurred, only 9.5 named storms were expected; a strong El Niño did indeed occur.) So, the 2009 forecast also did well.


2010 Atlantic hurricane season forecast from the UK GloSea model
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 in 2007. The UK Met Office is the United Kingdom's version of our National Weather Service. Their 2010 Atlantic hurricane season forecast calls for 20 named storms, with a 70% chance the number will range between 13 and 27. They predict an ACE index of 204, which is about double the average ACE index.

I have high hopes for the UK Met Office forecast, since it is based on a promising new method--running a dynamical computer model of the global atmosphere-ocean system. The CSU forecast from Phil Klotzbach 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 HadGEM3 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 0.86° in longitude, 0.56° in latitude (about 62 km), and up to 85 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, 2010 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-two 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 twenty named storms for the remainder of this hurricane season. Of course, the exact timing and location of these twenty 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 1989-2002, and coming up with correction factors (i.e., "fudge" factors) that give a reasonable forecast.

The future of seasonal hurricane forecasts using global dynamical computer models is bright. Their first three forecasts have been good. Last year the Met Office forecast was for 6 named storms and an ACE index of 60. The actual number of storms was 9, and the ACE index was 53. Their 2008 forecast called for 15 named storms, and 15 were observed. Their 2007 forecast called for 10 named storms in July - November, and 13 formed. 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.

2010 Atlantic hurricane season forecast from Florida State University
Last year, another group using dynamical computer forecast models entered the seasonal hurricane prediction fray. A group at Florida State University led by Dr. Tim LaRow introduced a new model called COAPS, which is funded by a 5-year, $6.2 million grant from NOAA. This year, the COAPS model is calling for 17 named storms and 10 hurricanes. Last year's prediction by the COAPS model was for 8 named storms and 4 hurricanes, which was very close to the observed 9 named storms and 3 hurricanes.

Summary of 2010 Atlantic hurricane season forecasts
Here are the number of named storms, hurricanes, and intense hurricanes predicted by the various forecasters:

23 named storms: PSU statistical model
20 named storms: UKMET GloSea dynamical model
18.5 named storms, 11 hurricanes, 5 major hurricanes: NOAA hybrid statistical/dynamical model technique
18 named storms, 10 hurricanes, 5 intense hurricanes: CSU statistical model (Phil Klotzbach/Bill Gray)
17.7 named storms, 9.5 hurricanes, 4.4 intense hurricanes: Tropical Storm Risk (TSR), hybrid statistical/dynamical model technique
17 named storms, 10 hurricanes: FSU dynamical model
10 named storms, 6 hurricanes, 2 intense hurricanes: climatology

Only four hurricane seasons since 1851 have had as many as nineteen named storms, so 5 out of 6 of these pre-season forecasts are calling for a top-five busiest season in history. One thing is for sure, though--this year won't be able to compete with the Hurricane Season of 2005 for early season activity--that year already had five named storm by this point in the season, including two major hurricanes (Dennis and Emily.)

Tropical Storm Conson threatens the Philippines
Weather456 has an interesting post on why the Western Pacific typhoon season has been exceptionally inactive this year. It looks like we'll have out first typhoon of the Western Pacific season later today, since Tropical Storm Conson appears poised to undergo rapid intensification, and should strike the main Philippine island of Luzon as a Category 1 or 2 typhoon.

Next post
I'll have an update Wednesday.

Jeff Masters

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Quoting largeeyes:
I'm curious. Am I the only person who has went back and read some of the 2005 blogs? Amazing the small number of comments there. Some of it is really amazing to read. I loved how Dr. Masters declared the season over, only to have to talk about Zeta on Dec 30.
How do you go back to some of the old blogs?.Can you give me a link.
Quoting CaribbeanIslandStorm:

All these waves coming off of africa seem to be dyeing out!
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1712. angiest
Quoting BFG308:
He'll always come back though. It makes no difference if he calls himself CBS4, WSVN, BermudaHigh, whatever it doesn't really matter. Just leave us alone seriously...

Anyway, as far as warming trends go, would it be fair to say the Iceland volcano eruption (future further eruptions) could aid in cooling on a short scale? Anyone know what time frame before eruptions have an effect on climate?


The Icelandic volcano has not actually been very bad, it is just in a bad position. More powerful volcanic eruptions have had negligible impact on climate (Mt. St. Helens), and significantly larger eruptions have had pretty major impact on climate (Pinatubo, Krakatoa, Tambora). IMHO, there won't be any major impact from Iceland (subject to change, of course).
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btwntx08,looks like nature knows we need a break.Someone from above is looking out for us.
bob had it in the gulf by friday just s.w. of florida
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Quoting Baltimorebirds:
Is it from that current feature over the bahamas.
yes, it sure is. he said the high will move out and the low will move in. i wonder if it will develop into anything. any models on that Bahamas feature? thanks in advance :)
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I'm curious. Am I the only person who has went back and read some of the 2005 blogs? Amazing the small number of comments there. Some of it is really amazing to read. I loved how Dr. Masters declared the season over, only to have to talk about Zeta on Dec 30.
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Member Since: July 13, 2008 Posts: 6 Comments: 10796
1705. IKE
Parallel GFS 12Z @ 84 hours....not in agreement with the NAM....I'm shocked....

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Quoting Baltimorebirds:
That's interesting.Looks like it could impact the oil spill.

actually the gulf oil spill would be spared again looks like it moves w/wnw on the run
Member Since: July 13, 2008 Posts: 6 Comments: 10796
Post unnecessary now...
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Quoting sarahjola:
yeah, bob breck on fox 8 news in new orleans says theres going to be a low in the gulf just s.w. of florida.:)
Is it from that current feature over the bahamas.
1701. WSVN
hey there, adrian! we've got dangerous times coming up, don't we? gulp.
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1699. WSVN
:)
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Quoting StormW:
REGIONAL EFFECTS OF ENSO ON U.S. HURRICANE LANDFALLS


FSU TC Return Period Calculator
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new picture of this wave.
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Quoting StormW:
REGIONAL EFFECTS OF ENSO ON U.S. HURRICANE LANDFALLS


On that note, I noticed below that you made a reference to more "southern and western tracks" during La Nina years......I agree with the more western tracks, or westernmost development, if you will but I thought that La Nina years historically increase US East Coast probabilities a bit, hence, slighlty more Northern tracks at some point which can impact from the FL/GA border northward..............
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more ridging on the east coast in august watch out east coast for a few hurricanes to hit land there.
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Quoting kshipre1:
Dear Dr. Masters,

Hello. My name is Prerak Dave. I just joined the weather underground blog yesterday. I am proud to be a part of this. I love your blogs that you write. Very interesting.

I was wondering if you can answer something for me. In your opinion, why do you think we have only 1 named storm so far? Many forecasting agencies say that the tropical conditions are worse than 2005. Obviously is this good because we do not want any hurricanes. However, at what point do you think tropical activity will pick up? What exactly is inhibiting tropical/hurricane formation right now? Are you adjusting your forecast due to it being so quiet?

I know the active season does not start for another month but just comparing to 2005.

Thank you Dr. Masters and I look forward to hearing from you. I am happy to be a part of weather underground. Take care.

Welcome to Weather Underground. The current quiet spell in the Atlantic will last another 7-10 days. Blame the quiet spell on the stronger trade winds off Africa, blowing tons of dust and dry air into the Atlantic.

As the -NAO (Negative North Atlantic Ossolation) will cause the Azores-Bermuda High in the Central Atlantic to weaken, allowing trade winds to decrease, which will slow or stop the Sahara Air Layer (SAL-dry air over the Atlantic).

As the air moistens up over the MDR (main development region) the tropical waves that come off of Africa will have much more moisture to work with. Plus, this is the time of the year where the ITCZ (Inter-tropical convergence zone) moves northward, towards 10-12N latitude, allowing stronger waves to come off the African continent.

Computer models are hinting at possible Tropical Cyclone (TC) development in 7-10 days.
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Baltimorebirds:
That's interesting.Looks like it could impact the oil spill.
yeah, bob breck on fox 8 news in new orleans says theres going to be a low in the gulf just s.w. of florida.:)
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its going to get hot again on the east coast this week temp around 94F ALL WEEK LONG..in conn..
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Quoting stormhank:
Storm..I know this is hard to determine way out in the future but if you had to make a prediction.. how would you say the BH will set up this season?? east coast 2004, 2005.. or like in 2006 when storms recurved
I'm not storm,but I can tell you the bermuda high has been positioned further south than normal.of course it can change over the season.
Quoting StormW:


If I'm correct, the more ridging implies that there is some ridging over the western Atlantic, or in our case so far, over the eastern and central U.S., whereas in a positive NAO, we have one big strong A/B high. If you notice how the ridge over the 4 corners region is weaker, during a negative NAO it's usually off the east coast, or close to the east coast, at the strength it's at, or weaker. Right now, looking at this, the A/B high is a little stronger, indicative of the positive NAO we are currently in, and there is a more pronounced trof off the east coast. When we slide back to a negative NAO, that ridge out west should shift east, as well as the center of the A/B high.

Storm..I know this is hard to determine way out in the future but if you had to make a prediction.. how would you say the BH will set up this season?? east coast 2004, 2005.. or like in 2006 when storms recurved
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Do you need to insult people?.you know who I'm talking about jfv.
StormW I have a question (or 2) for you. Based on the NAO chart below, it seems the forecast would have us somewhere around -5 to -1 later this month. Did I read this correct? Also, how much will this affect SAL? Will it clear it out? Finally, what will this do to tracks of developing systems? Sorry if all this has been answered already but I just got on and seen the MJO was about to really unload on us and wondered how a negative NAO would impact us as well. I know that it means more likelyhood of developement, just not so sure about what you can expect at the various negative number ranges.
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It's like a Hurricane version of Romper Room in here right now with all the questions and answers by the Senior Chief......Perhaps "Mr. Storms Neighborhood".........God Bless Him.
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Quoting nrtiwlnvragn:
Not sayin I believe it, 12Z NAM 84 hours (system from the Bahamas).



oh my lol interesting
Member Since: July 13, 2008 Posts: 6 Comments: 10796
Quoting NRAamy:
GoodOleBudSir....just in time....


:)


I see that!
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Oh as you all can see I can work that quote button now...thank u all for the info on that..amazing at what you can learn in WU chats lol
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Dear Dr. Masters,

Hello. My name is Prerak Dave. I just joined the weather underground blog yesterday. I am proud to be a part of this. I love your blogs that you write. Very interesting.

I was wondering if you can answer something for me. In your opinion, why do you think we have only 1 named storm so far? Many forecasting agencies say that the tropical conditions are worse than 2005. Obviously is this good because we do not want any hurricanes. However, at what point do you think tropical activity will pick up? What exactly is inhibiting tropical/hurricane formation right now? Are you adjusting your forecast due to it being so quiet?

I know the active season does not start for another month but just comparing to 2005.

Thank you Dr. Masters and I look forward to hearing from you. I am happy to be a part of weather underground. Take care.
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1678. NRAamy
GoodOleBudSir....just in time....


:)
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1675. BFG308
He'll always come back though. It makes no difference if he calls himself CBS4, WSVN, BermudaHigh, whatever it doesn't really matter. Just leave us alone seriously...

Anyway, as far as warming trends go, would it be fair to say the Iceland volcano eruption (future further eruptions) could aid in cooling on a short scale? Anyone know what time frame before eruptions have an effect on climate?
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Seems very possible from what Ive read La Nina would be in place for active part of this season..does that normally mean more land falling storms with less recurvature???
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Quoting WSVN:
You wouldn't know absolutely anything about that type of a cuisine there, now would you, Amy? That's a Cuban dish, zangana! Something that you'll be light-years away from saverring, if ever, that is. I bet you do not even know what type of rice that is called right there? Anyways, that was food from a very sophisticated gala that I had attended, not too long ago. You do not know what your missing out onn, in that respect, of course, zorra y acerona, ^_^.


Did you wear the infamous tux?
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1671. SQUAWK
AMY!!!!
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1670. NRAamy
hey BB....

:)
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Quoting IKE:


Problem there is ....when one person quotes him it shows up on the blog for everyone to see.

There's no way to rid ourselves of him. It's like a bad zit that you just can't get the head to pop.



EEEWWWW YUCK
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Quoting NRAamy:



did you use the My Little Pony Shower Curtain as a table cloth for your dinner?
that dish looks good NRA lol
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1666. 7544
so if that high sets up where everyone is saying in augest it will not bode well for the so fla or the se is that correct ?
Member Since: May 6, 2007 Posts: 0 Comments: 6871
1665. IKE
Quoting stormhank:
anyone have a link to the parallel GFS model site...Im using the GFS site from model analysis site that also has the NAM model??
Link
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anyone have a link to the parallel GFS model site...Im using the GFS site from model analysis site that also has the NAM model??
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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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