Sep 27, 2011

DAY 119

Ophelia is back to life as a tropical depression. A Hurricane Hunter recon mission this afternoon found a closed surface circulation and sustained winds that were not quite strong enough to classify Ophelia as a tropical storm. There is still some dry air around her, but not as bad as it's been. Right now Ophelia is working on her upper divergence as she moves slowly WNW at 5 mph. You can see the upper-level clouds moving in a clockwise motion on her west side. That is a process of ventilation that is essential to a strengthening tropical system. As that air aloft moves quickly away, air from the surface moves upward to fill the space and lowers surface pressure. Rising moist air, creates condensation which releases latent heat. That latent heat is the fuel for the process to continue. This is the "positive feedback loop" that creates a hurricane.
(Tropical Depression Ophelia)
And a hurricane is what Ophelia is still destine to become. The Hurricane Center is forecasting a tropical storm by tomorrow, and a hurricane by Friday. The track for Ophelia is pretty much due north, despite the presence of a high pressure system there at the moment. But with the troughs sweeping off of the US coast, there isn't anywhere else for her to go. All the the forecast models support this movement, although some of them suggest further movement to the WNW for another day or so first.

As of tonight, Ophelia is bringing some stormy conditions to the Antilles Islands. You can see her building some thunderstorms right over some of the islands. Recon data was showing the stronger winds and rain well to the northeast of the islands however, and the NHC has not issued any watches or warnings as of 10pm eastern. Probably just light rain and gusty conditions there for right now.

(TD Ophelia)

Tropical Storm Philippe ran into quite a bit more dry air than was expected. That fact, coupled with some moderate westerly wind shear, has left Philippe with a structure that we have seen many times this season. A fairly empty swirl, void of convection. But he is still way out in the east Atlantic, so he's got plenty of time to come and go.

(Tropical Storm Philippe)
The forecast for Philippe is going to be changing quite a bit over the next few days. The Hurricane Center has changed their track to guide Philippe to the WNW for several days now, instead of an eventual turn to the east. That part of the Atlantic ocean has never been very conducive for tropical systems to strengthen. We may see Philippe go in and out of tropical storm status as he meanders out at sea of a few days. The forecast track for Philippe may change a few more times as well, although the computer models are supporting the NHC's new track.

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