The 2012 Hurricane Outlook

The Atlantic Basin has the most variable hurricane activity in the world and thus has become a challenge for meteorologists.  There seems to be a fascination with knowing what the season will be like, even if you can’t forecast where they may strike.

The Tropical Meteorology Project at Colorado State University has been making forecasts of the Atlantic hurricane seasons for the past 29 years.  It explains the need to forecast hurricane seasons this way:

“We issue these forecasts to satisfy the curiosity of the general public and to bring attention to the hurricane problem. There is a general interest in knowing what the odds are for an active or inactive season. One must remember that our forecasts are based on the premise that those global oceanic and atmospheric conditions which preceded comparatively active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons. This is not always true for individual seasons. It is also important that the reader appreciate that these seasonal forecasts are based on statistical schemes which, owing to their intrinsically probabilistic nature, will fail in some years. Moreover, these forecasts do not specifically predict where within the Atlantic basin these storms will strike. The probability of landfall for any one location along the coast is very low and reflects the fact that, in any one season, most U.S. coastal areas will not feel the effects of a hurricane no matter how active the individual season is.”

Image Credit: SCMED Operations Center.

Every year South Carolina gears up for the expectation of hurricanes.  The state has a state-of-the-art facility to monitor hurricanes and emergency events.  Plans are reviewed and renewed.  Everyone is encouraged to become aware of their local situation and if need be know what routes are to be used for evacuations.  It is important to have hurricane kits and to update them each year.  This is also important for land-lovers since the effects of hurricanes can extend far inland.

What is on tap for 2012?

The number of groups now forecasting hurricane season as grown recently.  The numbers have become a spectator sport and each group is trying to out-do the other.  I will focus on three different groups because of their method of forecasting.

The first is obviously the one doing it the longest, Colorado State University (CSU).  Their first outlook was issued in 1984 and it showed some promise.  The forecast method is a statistical one which looks for prior conditions and makes a statistical forecast of the odds of tropical activity.  They often refine this by looking for analogues to upcoming seasons.  Lately forecasts have also included the odds of landfalling hurricanes along segments of the coast.

The National Hurricane Center (NHC) began forecasting hurricane seasons a couple of decades after CSU.  Their method was based partly on the work from CSU, but also combined output from the dynamical computer models to create a hybrid statistical/dynamic forecast.

Finally, The Center for Ocean-Atmospheric Prediction Studies (COAPS) at Florida State University began issuing forecasts in 2009 based on a computer model developed at COAPS.  In their press release they state:

“The scientists use a numerical atmospheric model developed at COAPS to understand seasonal predictability of hurricane activity. The model is one of only a handful of numerical models in the world being used to study seasonal hurricane activity and is different from the statistical methods used by other seasonal hurricane forecasters. FSU is the only university in the United States issuing a seasonal hurricane forecast using a global numerical atmospheric model. The model uses the high performance computers at FSU to make predictions of the atmosphere six months into the future. Based on these atmospheric predictions, tropical activity is objectively determined and forecasts are issued around June 1st.”

Ok, so what at the forecasts?

Organization	Release Date	Method of Forecasting	Named Storms	Hurricanes	Major Hurricanes
CSU	6/1/12	Statistical	13	5	2
NHC	5/25/12	Hybrid	9-15	4-8	1-3
COAPS	5/30/12	Dynamical	10-16	5-9	*

·         COAPS does not forecast the number of major hurricanes (category 3-4-5).

NHC and COAPS give their forecasts in ranges which correspond to their 70% chance of occurrence which makes it difficult to compare with CSU.  However, using the CSU prediction does have some uncertainty.  It is expressed as “…(we) expect to see 2/3 of our forecasts verify within one standard deviation of observed values, with 95% of forecasts verifying within two standard deviations of observed values.”

Here is a comparison using the ranges:

Organization	Release Date	Method of Forecasting	Named Storms	Hurricanes	Major Hurricanes
CSU	6/1/12	Statistical	9.3-16.7	2.9-7.1	0.4-3.6
NHC	5/25/12	Hybrid	9-15	4-8	1-3
COAPS	5/30/12	Dynamical	10-16	5-9	*

·         COAPS does not forecast the number of major hurricanes (category 3-4-5).

What may influence the hurricane season?

A good review of the meteorological and oceanographic influences are summarized in the paper from CSU (click here to view).  Briefly, they include wind shear, sea-surface temperatures, and El Nino.

The back-to-back La Nina conditions have ended and we are now in a neutral phase.  The great uncertainty is when does El Nino make an appearance.  If it is late summer, then the activity will be on the low side.

This year is not expected to be as active as last year.  The primary reason is that sea-surface temperatures are lower especially in the eastern tropical Atlantic.

Sea surface temperatures anomalies for May 2012.  Image Credit: Climate Central.

Sea-surface temperature anomalies are only part of the equation, but can have a significant influence.  Contrast an active year like 2005 with an inactive year like 1991.  There was a significant difference in sea-surface temperatures.

Image Credit: Climate Central.

Bottomline:  This is likely to be near normal as far as the number of hurricanes are concerned.  Most of the development will be in the western Atlantic, Caribbean, or Gulf of Mexico.  The Cape Verde season may not amount to much.  As always, be on guard.