2012 Atlantic hurricane season forecast

By: TropicalAnalystwx13 , 08:32 PM GMT on mai 08, 2012

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Introduction

The 2012 Atlantic hurricane season is expected to be near or slightly above the long-term average with 12 named storms, 6 hurricanes, and 3 major hurricanes. Significant factors contributing to this decrease in tropical cyclone activity, compared to previous years, include the dissipation of La Niña in the equatorial Pacific Ocean, above normal Sea Level Pressures, rainfall patterns in the Atlantic and above normal Sea Surface Temperatures.


Figure 1. My predicted numbers compared to other forecasting agencies.

Landfall Risk

  • Entire U.S. coastline – 51% (average for last century is 52%)
  • U.S. East Coast – 23% (average for last century is 31%)
  • U.S. Gulf Coast – 41% (average for last century is 30%)
  • Expected near average major hurricane landfall risk in the Caribbean Sea
Significant Indicators
  • El Niño-Southern Oscillation & Vertical Wind Shear Relationship
  • Rainfall Patterns over West Africa & Tropical Atlantic Relationship
  • North Atlantic Oscillation & Mean Sea Level Pressure Relationship
  • Sea Surface Temperatures
The Basics

EL NIÑO-SOUTHERN OSCILLATION/VERTICAL WIND SHEAR

El Nino-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five year. During El Niño, high Sea Surface Temperatures across the East Pacific generates intense thunderstorm activity. As a result, outflow produced by those thunderstorms enhances westerly wind shear across the Gulf of Mexico, Caribbean Sea, and Western Atlantic. This provides generally favorable conditions for tropical cyclogenesis in the Pacific. Oppositely, during Neutrals and weak to moderate La Niña, above average Sea Surface Temperatures in the Atlantic generate intense thunderstorm activity that produces significant outflow aloft, providing high vertical wind shear across the Pacific. This provides generally favorable conditions for tropical cyclogenesis in the Atlantic.

RAINFALL PATTERNS OVER WEST SAHEL/TROPICAL ATLANTIC

West Africa is the birthplace for most Atlantic tropical cyclones. In addition, it is also the origin of the West African Dust outbreaks known as the Sahara Air Layer. Wetter than normal conditions across the Sahel argue for wetter and more convective tropical waves, and also prevent major SAL outbreaks during the season. Drier than normal conditions produce hotter tropical waves that weaken as they move into the East Atlantic due to an unfavorable temperature gradient. This also means many major SAL outbreaks are likely during the season.

A wetter atmosphere across the Atlantic is typically indicative of Madden-Julian Oscillation, or MJO, in its upward phase. During this phase, tropical cyclogenesis is enhanced as instability remains high and convection is encouraged. A drier atmosphere is typically indicative of a downward phase of the MJO, which reduces vertical instability and suppresses convection. Uncommonly, tropical cyclones do form during the downward phase of the MJO.

NORTH ATLANTIC OSCILLATION/MEAN SEA LEVEL PRESSURE

There are two phases of the North Atlantic Oscillation: positive and negative. A positive North Atlantic Oscillation (NAO) implies a stronger subtropical ridge in the Atlantic and deeper than normal Icelandic low. The negative NAO phase indicates a weaker than normal subtropical ridge and shallower than normal Icelandic low. The positive phase of the NAO reduces Sea Surface Temperatures in the Atlantic due to increased evaporational cooling, while the negative phase of the NAO increases Sea Surface Temperature due to decreased evaporational cooling.

The negative NAO typically enhances tropical cyclone activity in the Atlantic due to weaker trade winds, while a positive NAO typically suppresses tropical cyclone activity due to stronger than normal trade winds that can not only act to shear the system, but prevent the disturbance from attaining a well-defined center.

The positive NAO correlates with above average Mean Sea Level Pressure (MSLP) which is unfavorable for tropical cyclogenesis, while a negative NAO correlates with below average MSLP which enhances tropical cyclogenesis.

SEA SURFACE TEMPERATURES

Sea Surface Temperatures have an enormous effect on the peak intensities of tropical cyclones and usually determine whether a system is tropical or subtropical. Values below 26 °C aren’t typically warm enough for tropical cyclones, and cyclones typically develop as subtropical cyclones. Values above that are conducive for tropical cyclone development.

Expected in 2012



Analogue years

In order to retrieve analogue years for a particular hurricane season, I compare different historical ENSO cycles that resembled weather patterns similar to that of the winter and early spring of 2012. Using that technique, I came up with quite a few analogue years: 1951, 1957, 1965, 2002, and to a lesser extent, 2004. The average of all aforementioned hurricane seasons give us 12.75 named storms, 5.6 hurricanes, and 3.2 hurricanes. I have taken the lower values of all these numbers due to the uncertainty pertaining to whether or not El Niño will surface during the season.

Summary

In short, the motto for this hurricane season is that there will be less named storms overall, but there is an increased chance for USA landfalls. An early start to the hurricane season appears likely, and an early end to the hurricane season is plausible, especially if El Niño surfaces in the equatorial Pacific. I am expecting 12 named storms, of which 6 will strengthen into hurricanes, and of which 3 will intensify into major hurricanes, or hurricanes with maximum sustained winds greater than 111 mph.

Thanks for reading,

TropicalAnalystwx13

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17. stormhank
09:30 PM GMT on mai 09, 2012
thanks bro..good job
Member Since: septembrie 8, 2005 Posts: 0 Comments: 1386
16. Thrawst
11:53 PM GMT on mai 08, 2012
This will surely be an interesting season... nice update!
Member Since: iulie 18, 2010 Posts: 50 Comments: 1909
15. TropicalAnalystwx13
11:42 PM GMT on mai 08, 2012
Again, thanks for stopping by everybody!
Member Since: iulie 6, 2010 Posts: 113 Comments: 32717
14. AtHomeInTX
11:26 PM GMT on mai 08, 2012
Great Job! It's going to be interesting to hear from you when we have a storm out there too. Looking forward to it. :)
Member Since: august 24, 2010 Posts: 0 Comments: 253
13. OrchidGrower
11:12 PM GMT on mai 08, 2012
Very good write-up....'Far as I'm concerned, feel free to share your analyses with us as the 2012 storm season progresses; your insights will be appreciated!
Member Since: septembrie 24, 2002 Posts: 0 Comments: 396
12. Ameister12
09:41 PM GMT on mai 08, 2012
Very nice blog, TropicalAnalyst. Let's see if your forecast is correct. ;)
Member Since: august 9, 2009 Posts: 10 Comments: 5080
10. weatherh98
08:58 PM GMT on mai 08, 2012
Quoting TropicalAnalystwx13:

I may do another one in August, but I'm not sure yet.

Id say do one in late june and into august
Member Since: iunie 17, 2011 Posts: 11 Comments: 6539
9. weatherh98
08:57 PM GMT on mai 08, 2012
Thanks, Learning stuff from the kid:)
Member Since: iunie 17, 2011 Posts: 11 Comments: 6539
8. TropicalAnalystwx13
08:54 PM GMT on mai 08, 2012
Quoting Tropicsweatherpr:
13,this will be your only forecast or you are going to make updates to it down the road as CSU,TSR and NOAA do?

I may do another one in August, but I'm not sure yet.
Member Since: iulie 6, 2010 Posts: 113 Comments: 32717
7. Tropicsweatherpr
08:52 PM GMT on mai 08, 2012
13,this will be your only forecast or you are going to make updates to it down the road as CSU,TSR and NOAA do?
Member Since: aprilie 29, 2009 Posts: 75 Comments: 14777
6. TropicalAnalystwx13
08:49 PM GMT on mai 08, 2012
Quoting Grothar:
You are getting better with each season. Very good analysis. You have gotten almost everything covered. You even force me to plus this one.

Haha, thanks for stopping by Gro.

Everybody else as well.
Member Since: iulie 6, 2010 Posts: 113 Comments: 32717
5. Grothar
08:46 PM GMT on mai 08, 2012
You are getting better with each season. Very good analysis. You have gotten almost everything covered. You even force me to plus this one.
Member Since: iulie 17, 2009 Posts: 71 Comments: 27125
4. MAweatherboy1
08:44 PM GMT on mai 08, 2012
Great blog TA 13! I agree with just about everything you said... My numbers are about the same as yours... I'm thinking 11-5-2.
Member Since: februarie 11, 2012 Posts: 84 Comments: 8002
3. nigel20
08:42 PM GMT on mai 08, 2012
Nice update TAwx13...lets see if you're correct over the coming months
Member Since: noiembrie 6, 2010 Posts: 12 Comments: 8424
2. Tropicsweatherpr
08:40 PM GMT on mai 08, 2012
That is a great writeup of your forecast that has all the factors that will be key for TC formation in the North Atlantic basin. And I agree on the numbers. Mines are 12/7/3.
Member Since: aprilie 29, 2009 Posts: 75 Comments: 14777
1. CybrTeddy
08:39 PM GMT on mai 08, 2012
Excellent update!!
Member Since: iulie 8, 2005 Posts: 259 Comments: 24553

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About TropicalAnalystwx13

Teenager. Weather aficionado. Soccer fan. Realist. Posts subject to sarcasm. Goal: National Hurricane Center.