Time's almost up for Ernesto

The latest Hurricane Hunter report from 3:17 pm continues to indicate that Ernesto is not strengthening. The surface pressure remains steady at 1005 mb, and the maximum sustained surface winds steady at 45 mph. Ernesto's appearance on satellite imagery is still improving, with upper-level outflow being established to the north, and the size and depth of heavy thunderstorm activity increasing.
Key West radar animations show an increase in organization and intensity of the spiral rain bands. Ernesto still has until midnight to intensify, and should come ashore in the Everglades tonight with peak winds of 60 mph or lower.

Marathon in the Keys has had several heavy squalls go through, and reported a peak wind gust of 32 mph so far this afternoon. Top winds at some of the offshore buoys have been 35 mph, gusting to 40 mph.

Forecast track
There is no change to the forecast for Florida, landfall will be tonight near midnight in the Everglades, followed by a 1-day long plus passage up the length of Florida, followed by a re-emergence into the Atlantic on Wednesday night or Thursday morning. Ernesto will re-intensify over water. If the storm stays close to shore and makes landfall in South Carolina, it will probably come ashore Thursday night as a tropical storm. This is the solution of the GFDL model. If the storm moves more offshore and makes landfall near the Outer Banks of North Carolina, it has extra time over warmer water, and will probably be a Category 1 hurricane. This is the solution of the UKMET model and Canadian model. The GFS and NOGAPS models have a solution in between. The models differ markedly in what direction Ernesto will go after landfall, with several models taking Ernesto up the coast into New England, and several northwest into Ohio.

Spectacular imagery
Since yesterday, the GOES-East satellite has been in rapid scan mode where it delivers one satellite image per minute. For those of you on high-bandwidth connections, the animation of these images available at http://hadar.cira.colostate.edu/ramsdis/online/RSOgeflt.html (Colorado State University) is most impressive.


Figure 1. Visible satellite image from 2:30pm EDT 8/29/06 over the Atlantic. Image credit: Navy Research Lab.

Ignore the wave I said to pay attention to, and pay a little attention to the wave I said to ignore--and the wave I didn't even mention
The concentrated area of thunderstorms I mentioned this morning, halfway between Africa and the Lesser Antilles Islands, near 9N 36W, has fallen apart. I no longer expect development of this system. However, another tropical wave to its east, at 12N 28W, has developed a very pronounced rotation this afternoon, and has some heavy thunderstorm activity on its south side. This wave has potential for some slow development over the next few days as it moves west at 20 mph. It's under 15 knots of wind shear. The thunderstorm activity associated with this wave is being enhanced by a process known as upper-level divergence. When the the winds at high levels diverge (blow outward from a common center), then air from the surface must rise to fill the vacuum created. As this surface air rises, the moisture in it condenses, fueling thunderstorms. Thunderstorms created by this mechanism make a tropical disturbance look more impressive than it really is. The upper divergence will go away over the next 24 hours, reducing the amount of thunderstorm activity the wave has.

The large spiral of low clouds near 18N 43W that I said to ignore this morning may be worth watching yet, although I don't think it will ever develop. A small burst of heavy thunderstorms developed on the east side of the center of circulation this afternoon, and the wave is under low enough wind shear for development, 10 knots. However, water vapor satellite imagery shows this wave embedded in a large area of dry air and African dust that should preclude development for at least the next two days.

I may have a short update tonight in Ernesto puts on a burst of intensification.

Jeff Masters