Tropical Storm Ernesto is strengthening in the eastern Caribbean and is on track to enter the Gulf of Mexico in two days. Conditions appear to be favorable for development into a major hurricane (Saffir-Simpson category 3 or higher). Computer model tracks begin to diverge at 3 days out (Tuesday Aug. 29), but once a storm enters the Gulf, it's going to make landfall somewhere.
Here is a good site for long-range forecasts. Note that the track of Ernesto only grazes land features briefly, staying mostly over water, before getting into the Gulf. More on the flip...
Storms need a number of conditions to be favorable in order to develop into hurricanes:
(1) Warm sea-surface temperatures. Here is an index to the latest data for the Gulf of Mexico.
(2) An absence of wind shear. Wind shear is simply wind directions and/or speeds being different at different altitudes. Hurricanes need a smooth, uniformly flowing atmosphere at all altitudes. Here is the most recent National Hurricane Center technical discussion of Ernesto. They are signaling low wind shear a few days out and significant strengthening.
(3) Latitude. Coriolis forces are required to spin the wind field into a hurricane. That's why hurricanes never form at low latitudes, below 15 degrees.
Right now, the predicted location of Ernesto in a few days puts it in the southern Gulf, just when the wind shear is about to die down. The magic set of ingredients is at hand.
The chances of Ernesto hitting New Orleans is small because its track after entering the Gulf is uncertain. This is due to the unknown future development of an upper level low currently in the Pacific Northwest, as discussed here. A number of scenarios are possible. Should the anticipated hurricane aim toward Houston, the Space Shuttle Atlantis mission due to attempt launch tomorrow afternoon will have to be aborted early - a first of its kind event for our space program.
Obviously there are lots of potential political ramifications to the events forthcoming and our preparedness.