Weather Nerd

Gustav track still very uncertain

[NOTE: The Houston Chronicle‘s “SciGuy” and hurricane-blogger, Eric Berger, will be hosting a live chat about Gustav starting at 1:00 PM EDT.]

Berger wrote at 7:20 AM EDT this morning:

[T]he GFDL model still forecasts a northerly turn across Cuba’s western edge, bringing Gustav into Mississippi. … Yet four other models, all of them generally reliable, now bring the storm to Texas, or the Texas-Louisiana border. The official forecast has remained on Louisiana so far today. But if the GFDL jumps to the left later today, you can bet the official forecast will follow it in bringing the storm to Texas.

But then he added in a 10:50 AM update:

[S]ome of the models have swung back toward Louisiana this morning. … The flip-flopping of the models is normal, and reflects the fact that the computers don’t yet have a firm handle on the system. The data collected by the Hurricane Hunters today should provide some more consistency by tomorrow. Hopefully.

For what it’s worth, while other models have ping-ponged, the important GFDL has been trending gradually and steadily eastward — from a New Orleans landfall at 2pm yesterday, to a Mississippi landfall at 8pm yesterday, to a Mobile Bay landfall at 2am today, to a predicted landfall just east of Mobile Bay in the latest, 8am run.

As usual, the official NHC forecast isn’t ping-ponging quite as much as the models. The new track, as of 11am EDT, splits the difference between yesterday’s New Orleans-aimed tracks and this morning’s 5:00 AM track toward central Louisiana. It now predicts a landfall in east-central Louisiana, just a slight shift from six hours ago.

The currently forecasted scenario would bring a potentially hellacious storm surge into southeast Louisiana, as the powerful right-front quadrant would be directly over New Orleans and environs. But the exact forecast track, five days out, means very little, as the degree of uncertainty is extremely high. In the NHC’s words:

RELIABLE MODELS REMAIN ON EITHER SIDE OF THE FORECAST TRACK…SO ONE SHOULD NOT FOCUS ON THE EXACT OFFICIAL TRACK.

As Alan Sullivan says, “the evolution of steering currents is so uncertain that a wide range of possible courses and landfalls is conceivable.” Nor are steering currents the only factor causing uncertainty. As the NHC discussion says, “IT IS NOT CLEAR IF THE CENTER WILL PASS DIRECTLY OVER JAMAICA OR WILL HUG THE SOUTH OR NORTH COAST.” Land interaction with Jamaica’s mountains may have a big impact on both the track and intensity of Gustav.

As I said earlier, the fog of uncertainty surrounding Gustav is unlikely to lift today, for this and other reasons. Tomorrow morning is the first time when we might get a better concept of where this storm is headed.

Quoting the New Orleans Times-Picayune:

There’s a reason for experienced New Orleans area meteorologists to warn hurricane watchers not to put much stock in predictions of a storm’s ultimate landfall until it gets into the Gulf of Mexico, and Gustav continues to prove them right. …

Recent model runs have broadened the playing field, with potential “solutions” ranging from Gustav only reaching the Yucatan Peninsula on a westward path at five days to curving through the central Gulf and then heading east of Tallahassee, Fla. …

The bottom line … is that Louisiana residents — indeed, anyone living along the northern coast of the Gulf of Mexico — will have to wait several more days for a more probable prediction of where Gustav will make landfall.

Meanwhile, Tropical Storm Hanna has formed, and now there’s a new wave off Africa that could eventually become T.S. Ike. A quick glance at the Tropical Weather Outlook makes clear that the peak of hurricane season has definitely arrived.