EDITOR'S NOTE: This article was written prior to the formation of Tropical Storm Erin & Hurricane Dean.  These storms will be covered in later editions of the Jambalaya.

Meteorologists often talk about the impacts of El Niño and La Niña on tropical cyclones throughout the Atlantic Ocean basin.  As we approach the peak of the 2007 Hurricane Season, many members of the public are questioning what impact El Niño and La Niña will have on the rest of this hurricane season.

El Niño is the warming of the equatorial Pacific Ocean waters. El Niño, as it evolves, brings rise to greater vertical wind shear conditions across the Atlantic Ocean basin which hinder tropical cyclone formation.  Thus, El Niño's net effect translates to below normal tropical storms and hurricanes for the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico.  In contrast, La Niña is the cooling of the equatorial Pacific waters. La Niña, as it develops, causes the relaxation of vertical wind shear over the Atlantic waters, a favorable condition for tropical storms and hurricanes to develop.  Therefore, La Niña favors a much more active hurricane season for the Atlantic, Caribbean, and Gulf of Mexico waters.

Earlier this year in late May and early June, conditions in the equatorial Pacific Ocean were in a neutral phase (neither El Niño or La Niña conditions). Current sea surface temperature anomalies as of August 2, 2007, which show above and below normal water temperatures, can be viewed below:
 

This display can also be found on the NOAA/NESDIS website at:  http://www.osdpd.noaa.gov/PSB/EPS/SST/data/anomnight.8.2.2007.gif

Current conditions on the image appear to indicate neutral conditions or a weak La Niña, depending on which region you look at in the equatorial Pacific.

Twenty computer models from the International Research Institute that forecast El Niño/La Niña conditions for the peak hurricane season months of August, September, and October were also reviewed.  16 out of 20 models are indicating slight to moderate La Niña conditions during the peak of this year's hurricane season. The remainder of computer models show slight warm-neutral or very weak El Niño conditions.  Thus, the majority of computer models still forecast a weak La Niña to develop this hurricane season.

However, other conditions besides sea surface temperatures in the equatorial Pacific Ocean are factors in the Atlantic Ocean hurricane season.  One additional area of concern is the amount of Saharan dust moving across the tropical Atlantic.  Dust from storms in the Sahara Desert in Africa often move across portions of the Atlantic Ocean during hurricane seasons.  High levels of dust appear to inhibit tropical cyclone formation in the Atlantic.  So far this year, observed levels of dust are in the moderate category, indicating levels neither conducive nor destructive for the development of hurricanes.

Another condition that can affect tropical cyclone formation is the thermohaline circulation.  The thermohaline oceanic circulation is a worldwide ocean current.  The portion that affects our area of the globe begins between South America and Africa, crosses the equator, and heads northwestward into the Caribbean and through the Yucatan Channel.  The circulation then begins curving back into the Florida Straits, and then northeastward just off the east coast of the United States (known here as the Gulf Stream).  This thermohaline circulation, when stronger than usual, enhances tropical cyclone formation.  When the circulation is very strong, more intense, major hurricanes tend to develop.  For the 2007 hurricane season, a stronger-than-normal thermohaline circulation is still forecast.

Finally, NOAA’s most recent hurricane forecast calls for a very high 75% chance of an above-normal hurricane season, a 20% chance of a near-normal season, and only a 5% chance of a below-normal season.  Dr. Bill Gray and Philip J. Klotzbach of Colorado State University are forecasting a 44% chance for a major landfalling hurricane between the Florida panhandle and Brownsville, Texas, vs. the long-term average of 30%.   All of these factors indicate the public should remain vigilant throughout the rest of the 2007 hurricane season!.