CSU predicts a very active hurricane season: 16 storms, 9 hurricanes

By: Dr. Jeff Masters , 4:30 PM GMT on June 01, 2011

Share this Blog
6
+

A very active Atlantic hurricane season is on tap for 2011, according to the seasonal hurricane forecast issued June 1 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 16 named storms, 9 hurricanes, and 5 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 166% 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 14 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is identical to their April forecast. The forecast calls for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (48% chance, 31% chance is average) and the Gulf Coast (47% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also high, at 61% (42% is average.)

The forecasters cited four main reasons for an active season:

1) Neutral to weak La Niña conditions are expected during the most active portion of this year's hurricane season (August-October). This should lead to average to below average levels of vertical wind shear.

2) Above average May sea surface temperatures in the tropical Atlantic.

3) Below average surface pressures during May in the tropical Atlantic.

4) We are in the midst of a multi-decadal era of major hurricane activity, which began in 1995. Major hurricanes cause 80-85 percent of normalized hurricane damage.

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 weak La Niña conditions in the equatorial Eastern Pacific, and above-average tropical Atlantic and far north Atlantic SSTs during April - May. Those five years were 2008, which featured Hurricane Ike and Hurricane Gustav; 1996, which had two hurricanes that hit North Carolina, Fran and Bertha; 1989, which featured Category 5 Hurricane Hugo; 1981, a very average year with 12 named storms, 7 hurricanes, and 3 intense hurricanes; and 1951, a year that featured 6 major hurricanes. The mean activity for these five years was 12 named storms, 8 hurricanes, and 4 intense hurricanes.

How accurate are the June forecasts?
The June forecasts by the CSU team between 1998 and 2009 had a skill 19% - 30% higher than a "no-skill" climatology forecast for number of named storms, number of hurricanes, and the ACE index (Figure 1). 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. Unfortunately, the CSU June 1 forecasts do poorly at forecasting the number of major hurricanes (only 3% skill), and major hurricanes cause 80% - 85% of all hurricane damage (normalized to current population and wealth levels.) This year's June forecast uses a brand new formula never tried before, so there is no way to evaluate its performance. An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.41 to 0.62 for their June forecasts made between 1984 and 2010, which is respectable.


Figure 1. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August), using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.


Figure 2. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 2001-2010, using the Mean Square Skill Score (MSSS). The figure shows the results using two different climatologies: a fixed 50-year (1950 - 1999) climatology, and a 2001 - 2010 climatology. Skill is poor for forecasts issued in December and April, moderate for June forecasts, and good for August forecasts. Image credit: Tropical Storm Risk, Inc.

TSR predicts 25% more activity than normal
Expect the Atlantic hurricane season to be about 25% more active than usual, the British private forecasting firm Tropical Storm Risk, Inc. (TSR) said in their pre-season forecast issued on May 24. TSR calls for 14.2 named storms, 7.6 hurricanes, 3.6 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 124, which is 22% above average. Their May 24 forecast numbers are very close to their previous forecast issued in April. TSR predicts a moderate 55% chance that activity will rank in the top 1/3 of years historically, and a 59% chance that U.S. landfalling activity will be above average. TSR rates their skill level as 16-25% higher than a "no-skill" forecast made using climatology, though an independent assessment by the National Hurricane Center (Figure 1) gives them somewhat lower skill numbers.

TSR projects that 4.4 named storms will hit the U.S., with 1.9 of these being hurricanes. The averages from the 1950-2010 climatology are 3.1 named storms and 1.5 hurricanes. They rate their skill at making these June forecasts for U.S. landfalls at 7 - 11% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.3 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their forecast of an active season:

1) Their model predicts that sea surface temperatures will be 0.11°C warmer than average in August and September over the Main Development Region (MDR) for Atlantic hurricanes. They define this as the area between 10°N and 20°N, between the coast of Africa and Lesser Antilles Islands (20°W and 60°W). It is called the Main Development Region because virtually all African waves originate in this region. These African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.)

2) Their model predicts slower than normal trade winds in August and September over the Main Development Region (MDR). Trade winds are forecast to be 0.19 meters per second (about 0.4 mph) slower than average. This would create more spin for developing storms, and allow the oceans to warm up, due to reduced mixing of cold water from the depths and lower evaporational cooling.

FSU predicts a very active hurricane season: 17 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their third annual Atlantic hurricane season forecast today. This year's forecast calls for a 70% probability of 14-20 named storms and 8-10 hurricanes. The mean forecast is for 17 named storms, 9 hurricanes, and an accumulated cyclone energy (ACE) of 163. They cite warm tropical North Atlantic sea surface temperatures, a weakening of La Niña conditions, and the ongoing positive phase of the Atlantic Multi-decadal Oscillation as the major factors influencing their forecast.

Other seasonal forecasts
The UK Met Office's Glosea4 model is predicting a moderately more active season than normal, with 13 named storms and a ACE index of 151. The Cuba Institute of Meteorology is calling for 13 named storms and 7 hurricanes. NOAA predicts 15 named storms, 8 hurricanes, and 4.5 intense hurricanes. Pennsylvania State University predicts 16 named storms.

A surprise tropical disturbance for Florida
The Atlantic hurricane season is officially underway, and Mother Nature appears to be taking her cue from the calendar, as we have a surprise storm off the coast of Florida that is a threat to develop into a tropical depression later this week, after it crosses Florida into the Gulf of Mexico. An cluster of thunderstorms called a Mesoscale Convective System (MCS) pushed across southern New England early yesterday, emerged over the ocean, and rotated clockwise towards Florida, steered by a large high pressure system centered over Kentucky. The center of the disturbance stayed over the warm waters of the Gulf Stream, a region of low pressure developed, and intense thunderstorms began to build yesterday afternoon. Early this morning, the National Hurricane Center (NHC) designated the disturbance Invest 93L, and gave it a 10% chance of developing into a tropical depression. At 8am EDT, they upped those chances to 30%. Invest 93L is becoming increasingly organized, with Melbourne, Florida radar showing the beginnings of some rotation, with a solid band of heavy rain on the southwest side of the disturbance. The pressure and winds have leveled out at Buoy 41012, 40 nm ENE of St. Augustine, Florida. Winds peaked at 19 mph, gusting to 22 mph, at 10:50am EDT. Satellite imagery shows a small but intensifying region of thunderstorms. Sea surface temperatures (SSTs) are about 26°C (79°F) off the east coast of Florida, which is just warm enough to support formation of a tropical depression, and about 0.5°C above average. Wind shear is a low 5 - 10 knots, and it is likely that 93L will continue intensifying until it makes landfall over Central Florida this afternoon. A 50-mile wide swath of Florida from Daytona Beach to just north of Tampa can expect 1 - 3 inches of rain from 93L as it tracks over the state this afternoon and tonight. A Windsat pass this morning did not show a closed circulation, and I doubt 93L has enough time to develop into a tropical depression before landfall in Florida. The coast between Daytona Beach and Cocoa Beach could see wind gusts of 25 - 35 mph this afternoon, though.


Figure 3. Afternoon radar image of 93L from the Melbourne, Florida radar.

Fate of 93L once in the Gulf of Mexico
Since 93L is expected to continue its rapid west-southwest motion at 15 - 20 mph through Thursday, it will cross the Florida Peninsula in about 12 hours and emerge over the Gulf of Mexico early Thursday morning. It is possible that the passage over Florida will greatly disrupt 93L, since it is such a small system. I give a 40% chance that the storm will see its peak strength this afternoon, and not significantly regenerate over the Gulf of Mexico. However, the latest SHIPS model forecast predicts that wind shear will remain low to moderate, 5 - 15 knots, as 93L moves westwards over the Gulf of Mexico Thursday and Friday. SSTs in the Gulf are about 27°C (81°F), 0.5 - 1.0°C above average, and it is possible that 93L could gain enough strength to become Tropical Depression One as it crosses the Gulf. Since 93L will be moving parallel to the coast a short distance offshore, it is difficult to predict where the storm might make a second landfall, since a slight change in heading will make a large difference in landfall location. I don't expect widespread heavy rains from 93L along the Gulf Coast, since the storm is so small, but some locations close to the coast could receive 2 - 4 inches as 93L brushes by. Heavier rains are possible at the eventual landfall location. Since 93L is so small, the computer models are having trouble seeing the system, and are not very helpful forecasting the behavior of the storm over the Gulf of Mexico. The Hurricane Hunters are on call to fly into 93L Thursday afternoon at 2pm EDT, if necessary.

Central Caribbean disturbance
Moisture and heavy thunderstorm activity continues to slowly increase in the region between Central America and Jamaica, and wind shear is falling. With wind shear now 20 - 30 knots, we can expect this disturbance to show increased organization today, and recent satellite images show the beginnings of a surface circulation trying to get going about 100 miles off the coast of Northeast Nicaragua. All of the computer models predict that an area of low pressure will form in this region by Thursday, and this low will have the potential to develop into a tropical depression late this week or early next week. A surge of moisture accompanying a tropical wave currently south of Hispaniola may aid development when the wave arrives in the Western Caribbean on Thursday. Water temperatures in the Central Caribbean are about 1°C above average, 29°C, which is plenty warm enough to support development of a tropical storm. Residents of Jamaica, Cuba, the Cayman Islands, Haiti, Honduras, and Nicaragua should anticipate the possibility that heavy rains of 2 - 4 inches may affect them Thursday through Saturday this week.


Figure 4. Satellite image of the Central Caribbean disturbance.

Catch my intro to the 2011 hurricane season on Internet radio
I'll be discussing the coming hurricane season on our Internet radio show, the Daily Downpour, tomorrow (Thursday) at 4:30pm EDT. Fellow wunderground meteorologists Shaun Tanner and Tim Roche will be hosting the show. We'll talk about the latest model runs, hurricane research, modeling accuracy, and hurricane climatology, and answer any questions listeners email in or call in. The email address to ask questions is broadcast@wunderground.com. Welcome to the hurricane season of 2011!

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 594 - 544

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Welcome to the Gulf of Mexico, 93L, enjoy your luxourous atmosphere, and feel free to become your maxium potential.

Member Since: Posts: Comments:
POSS T.C.F.A.
XX/XX/93L
MARK
28.55N/83.25W
Member Since: Posts: Comments:
Quoting RichardG:


www.wwlp.com is streaming live coverage showing video of a tornado going through southern edge of Springfield MA.

Wish I could watch, on my phone at work. Damage reports coming in now but very spotty. Evidently no one cares with all the tropical weather talk, but these are highly populated areas being impacted now. Here's a small article.
Link
Member Since: Posts: Comments:
Quoting alfabob:
#527 Buoys are hinting at a nearly closed surface circulation, Cedar Key (29.136 N 83.029 W) gusting at 30kts @330 degrees, winds offshore gusting at 8kts @270 (28.311 N 83.306 W), and then another on the coast gusting at 9kts @ 260 to 270 (28.433 N 82.667 W). This has both tropical and land characteristics, it will adapt better to the gulf then you think.
I observed a surface circulation as it passed over my pws. Winds throughout this morning were steady from the wnw, then w, now ssw
Member Since: Posts: Comments:
100 °F is cold!

Now, 86 °F is hot!

lol.
Member Since: Posts: Comments:
Tropics coming out with a vengeance, Carribean trying to blow wide open, frigin MCV turns around and plows itself towards the gulf and develops, next thing you know a cat 5 will be breaking down the door somewhere
Member Since: Posts: Comments:
587. Skyepony (Mod)
Quoting Patrap:
Much Improved Dvorak from earlier as well




That is impressive for coming off land this time of day..that's in the heat of the afternoon & not over land like seabreeze induced. Wait about 6 hrs to see it really go off.
Member Since: Posts: Comments:
93L has been an impressive little storm. I think it has an alright chance.
Member Since: Posts: Comments:
Quoting IKE:
It's hot outside....



100.7 °F


Scattered Clouds

Action: Quote | Ignore User
Member Since: June 9, 2005 Posts: 23 Comments: 36140
Say it Aint so Ike!!
Member Since: Posts: Comments:
93L is a very small system. Its growth will be inhibited during its Fla peninsula passage. Wherever it ends up it will be a purely beneficial rainmaker. It can't get any better!
Member Since: May 26, 2011 Posts: 0 Comments: 1193
582. Skyepony (Mod)
Yeah Davis is another step up.

There was a fatality from that MCS that is now 93L..

1440 UNK SOLON JOHNSON IA 4181 9149 *** 1 FATAL *** NUMEROUS TREES DOWN. 1 CONFIRMED FATALITY DUE TO TREE FALLING ON A TENT AT LAKE MACBRIDE STATE PARK. (DVN)

I pointed out a few months ago about people camping in such weather.
Member Since: Posts: Comments:
I remember balls of convection last season too! Will that ball fizzle or will the low close off and sustain itself?
Member Since: Posts: Comments:
579. IKE
It's hot outside....


100.7 °F

Scattered Clouds
Member Since: Posts: Comments:
I think there is something to be said about the fact that 93L faded once it was coming onshore. Now that it has moved offshore, it flared back up again. Tropical systems, especially weak ones, lose any punch they have when moving onshore due to the sudden change in environment. It looks like the tropical-natured low has re-emerged over the Gulf and has responded with exploding convection. Tonight will be interesting because it will be over waters that are plenty warm for development and in a light shear environment for about the next 36 hours.
Member Since: Posts: Comments:
Much Improved Dvorak from earlier as well

Member Since: July 3, 2005 Posts: 420 Comments: 127536
I understand that even the low shear may shear it up a bit, that's why I put the chances at 50% for a name. Right now, it's holding it's own.
Member Since: Posts: Comments:
Quoting marknmelb:
Who has their own home weather station ??? Mine is really old and I need to replace it. Is there much of a diff between a LaCrosse or a Weatherwise system ???
I would suggest talking to Aquak9 or Rainman32.
Member Since: Posts: Comments:
From 18Z earlier

Member Since: July 3, 2005 Posts: 420 Comments: 127536
Member Since: July 17, 2009 Posts: 69 Comments: 25321
Quoting IceCoast:
Tornado reported .5 miles from downtown Springfield. Storm has since passed the area. Listening to local radio for more information but not much right now.


www.wwlp.com is streaming live coverage showing video of a tornado going through southern edge of Springfield MA.
Member Since: Posts: Comments:
What is 93L's current pressure?
Member Since: Posts: Comments:
Quoting Hurrykane:


Yes...

Deep layer:


Mid layer:
Thanks, Are either one or both favorable for 93L going into the GOM? Are they expected to change?
Member Since: Posts: Comments:
Quoting cchsweatherman:


Keep in mind the convective burst came as a result of the normal diurnal processes and instability over Florida. Once it enters the Gulf of Mexico, not only will it lose this energy source, but it will be meeting 10-15 kt wind shear which would be the highest shear it has faced its entire life time. For such a small system, any increase in shear could be crippling to it. No surface observations show a surface circulation in association with this system either.
It's not a closed circulation yet, but I don't know what you're talking about as far as sheer.

Here's the current sheer map



Sheer tendency



Sheer forecast at 24hrs



Sheer forecast at 48hrs




Conclusion - sheer is going down over the gomex and is forecasted to stay down.

As far as convection dying once it moves over land, I doubt that, since there is plenty of convective energy over the gulf


Member Since: Posts: Comments:
Member Since: July 3, 2005 Posts: 420 Comments: 127536
565. JRRP
Quoting eyestalker:
So basically, 94L's anticyclone is going to effectively push the subtropical jet north? That could also be a harbinger for later in the month/year because these shear walls don't start moving back south until October once they are pushed north.

94L?
Member Since: Posts: Comments:
Looks better than when it first moved over the east coast.

Member Since: July 17, 2009 Posts: 69 Comments: 25321
Quoting cchsweatherman:


Look at the flow of the shear. Throughout the entire life time of this system, it has been encountering upper level winds going in the same direction as the system which are favorable for a system. But now that its changing direction in motion, its encountering upper level winds around 15 kts from the southeast. This goes against the motion of the system.


The CIMSS wind shear charts don't take into account something very important with systems called speed shear. Speed shear occurs when a system outraces the upper level flow in the atmosphere causing a system to decouple and essentially lack true organization.
Member Since: Posts: Comments:
562. Skyepony (Mod)
Quoting marknmelb:
Who has their own home weather station ??? Mine is really old and I need to replace it. Is there much of a diff between a LaCrosse or a Weatherwise system ???


I went from a LaCrosse to a Tycon. The Tycon has lasted nearly twice as long so far.
Member Since: Posts: Comments:
93L Floater - Rainbow Color Infrared Loop
Member Since: July 3, 2005 Posts: 420 Comments: 127536
000
FZNT24 KNHC 012031
OFFNT4

OFFSHORE WATERS FORECAST FOR THE GULF OF MEXICO
NWS NATIONAL HURRICANE CENTER MIAMI FL
430 PM CDT WED JUN 01 2011

OFFSHORE WATERS FORECAST FOR THE GULF OF MEXICO

SEAS GIVEN AS SIGNIFICANT WAVE HEIGHT...WHICH IS THE AVERAGE
HEIGHT OF THE HIGHEST 1/3 OF THE WAVES. INDIVIDUAL WAVES MAY BE
MORE THAN TWICE THE SIGNIFICANT WAVE HEIGHT.

GMZ089-020330-
SYNOPSIS FOR THE GULF OF MEXICO
430 PM CDT WED JUN 01 2011

.SYNOPSIS...A SMALL LOW PRESSURE CENTER WILL MOVE W ALONG 29N
TONIGHT AND THU. OTHERWISE MODERATE TO FRESH TRADES WILL PERSIST
THROUGH MON BETWEEN AREAS OF HIGH PRES TO THE NORTH...AND LOW
PRES OVER THE CARIBBEAN. THE HIGHEST WINDS AND SEAS WILL REMAIN
IN THE SE GULF.
Member Since: May 27, 2009 Posts: 0 Comments: 4436
Tornado reported .5 miles from downtown Springfield. Storm has since passed the area. Listening to local radio for more information but not much right now.
Member Since: Posts: Comments:
557. HCW
Quoting marknmelb:
Who has their own home weather station ??? Mine is really old and I need to replace it. Is there much of a diff between a LaCrosse or a Weatherwise system ???


Go with a Davis weather station over the above garbage. It will last longer and give you more accurate readings
Member Since: Posts: Comments:
556. Skyepony (Mod)
Got a west wind there the buoy west of Spring Hill. The one just west of Spring hill on land is WSW. Just south of there it comes from out the East again.
Member Since: Posts: Comments:
Quoting TropicalAnalystwx13:
My hurricane season risk map...Please do not criticize me if you don't agree, and please don't criticize me for it being sloppy :)



You know that no one criticizes anyone on this blog. Very reasonable map.
Member Since: July 17, 2009 Posts: 69 Comments: 25321
Who has their own home weather station ??? Mine is really old and I need to replace it. Is there much of a diff between a LaCrosse or a Weatherwise system ???
Member Since: Posts: Comments:
Quoting fmhurricane2009:

Will 93L lose some foward speed, and if so by how much? Wouldn't it help the disturbance be more vertically stacked if it did (I just remembered Colin of last year, he was going so fast he lost it and then regenerated once it slowed down)

Thanks in advance for any input.


I think it should keep it's forward speed and travel around that edge of the high pressure system.
Member Since: Posts: Comments:
Are there different levels of shear in the atmosphere?
Member Since: Posts: Comments:
XX/XX/93L
Member Since: Posts: Comments:
Member Since: July 3, 2005 Posts: 420 Comments: 127536
Member Since: May 27, 2009 Posts: 0 Comments: 4436
Quoting cchsweatherman:


Look at the flow of the shear. Throughout the entire life time of this system, it has been encountering upper level winds going in the same direction as the system which are favorable for a system. But now that its changing direction in motion, its encountering upper level winds around 15 kts from the southeast. This goes against the motion of the system.


Good point, as the shear against it really stacks considering how fast 93L is going in the opposite direction. Needs to slow down.
Member Since: Posts: Comments:
Quoting Hurrykane:
Updated shear forecast



By the time the jet stream gets to that point 93L will be gone anyway.
Member Since: Posts: Comments:

Viewing: 594 - 544

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Overcast
69 °F
Overcast