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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2563. JLPR2
Quoting Drakoen:


Yes and it is happening consecutively.


Yep, two in a row now, I wonder if the one behind this one has a spin, anyone checked that out?
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Quoting helove2trac:
what does all this MEAN????? ridging pattern change


No, the ridging is still there. The moisture surge is all the way up to 20N, meaning a LLC around 10N would be greatly shielded from the SAL. This is a rather remarkable change as north of 10 has been dry as a bone thus far.
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2561. xcool
yayy .big mom wave and spin
Member Since: September 26, 2009 Posts: 2 Comments: 15648
looks like waves coming off at a higher latitude
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Quoting Drakoen:


Elaborate


The tropical wave coming off of Africa is embedded in an envelope of deep tropical moisture thanks to the wave ahead of it. In addition it is tapping moisture from ITCZ and lifting it poleward.
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2558. Drakoen
Quoting JLPR2:
Tropical waves are exiting Africa with a spin somewhere in their Axis?


Yes and it is happening consecutively.
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Quoting CyclonicVoyage:
A bunch of African's just save a bunch a money on their car insurance??

Close, a whole bunch of African ITCZ disturbances just saved money on their car insurance :o)
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2555. JLPR2
Tropical waves are exiting Africa with a spin somewhere in their Axis?
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2554. Patrap
Atlantic Invest..."Quint Eye's"
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Quoting StormW:


The development appears to be detached from the ITCZ
Yeah, that circulation looks way too north to be attached to the ITCZ.
Member Since: September 2, 2009 Posts: 130 Comments: 21121
2552. xcool
:0
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Chief: Radio check, over.
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2547. Patrap
Saharan Air Layer Analysis 5-Day Atlantic Movie
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2546. Drakoen
Quoting xcool:
spin


Elaborate
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Quoting Drakoen:
What going on with what is coming off Africa...


quoting xcool..... KABOOM
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2544. xcool
big wave and spin
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting CyclonicVoyage:
A bunch of African's just save a bunch a money on their car insurance??


Gieko caster
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2541. help4u
Experts,is the DGEX a realiable model?
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what does all this MEAN????? ridging pattern change
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2539. Patrap
Atlantic/latest_wv.jpg
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Quoting Drakoen:
What going on with what is coming off Africa...
Looks monsoonal.
Member Since: September 2, 2009 Posts: 130 Comments: 21121
Quoting Drakoen:
What going on with what is coming off Africa...


A surge of moisture...
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2536. xcool
spin
Member Since: September 26, 2009 Posts: 2 Comments: 15648
A bunch of African's just save a bunch a money on their car insurance??
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Member Since: September 2, 2009 Posts: 130 Comments: 21121
2533. Drakoen
What going on with what is coming off Africa...
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I tell you the convection really increased at the inverted V feature at about (the apex) at 38W..

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Quoting MiamiHurricanes09:
Looks like some nasty ridging to me.


Maybe. The whole sub-tropical Atlantic is spinning in an anti-cyclonic motion.
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2529. xcool
Madden - Julian Oscillation
Member Since: September 26, 2009 Posts: 2 Comments: 15648
2527. Drakoen
Nope
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Quoting CyclonicVoyage:


Some serious ridging out there mate.
That's what I'm thinking now.
Member Since: September 2, 2009 Posts: 130 Comments: 21121
Quoting Drakoen:


No, look at the Eastern Atlantic and Africa
Looks like some nasty ridging to me.
Member Since: September 2, 2009 Posts: 130 Comments: 21121
2523. xcool
Weather Research Center call for 8 named stoms hmm.
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting Drakoen:


No, look at the Eastern Atlantic and Africa


Moistening of the tropical Atlantic due to a series of tropical waves.
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2521. Drakoen
Quoting Ivanhater:
Looks like the ITCZ lifting up on the loop


Good guess, not what I am looking for though
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2520. xcool
get ready kaboom
Member Since: September 26, 2009 Posts: 2 Comments: 15648
what pattern is dat
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2518. Drakoen
Quoting MiamiHurricanes09:
Ooooooo, I like Drak trivia. I think you're speaking about the upper level pattern forecasted by the GFS in the eastern Atlantic. I'm probably wrong, but it's worth a try, lol.


No, look at the Eastern Atlantic and Africa
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Quoting CyclonicVoyage:


Unfortunately yes.
Ok, what is it?
Member Since: September 2, 2009 Posts: 130 Comments: 21121
Looks like the ITCZ lifting up on the loop
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Quoting Drakoen:
What is that pattern?


Some serious ridging out there mate.
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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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