Jul 28, 2011

DAY 57

Tropical Storm Don was born at 4pm eastern today just 2 hours after the National Hurricane Center released an advisory with a 100% chance of tropical cyclone development. At 2pm the system was so borderline that NHC decided to wait until the Hurricane Hunter recon mission was complete. They did find a closed center of circulation and sustained surface winds of 40 mph and Don was named.

Don will be hard pressed to become the seasons first Atlantic Hurricane. Atmospheric conditions are only marginally favorable for further development tomorrow. The forecast models have just started to come back around. I really don't know what happened to the HWRF and the GFDL. Both of them had this thing nailed on Saturday nights runs (as seen below) with a weak tropical storm just of the tip of the Yucatan valid for Wednesday night, and then NHC took 90L offline for almost an entire day. First it gives me great confidence in these 2 models to have nailed this one like that. But at the same time it worries me that they would lose it for a few days after that.

That's in the past though. As of 10pm eastern Don had sustained winds of 40 mph and a pressure of 1000 mb. He is continuing to move to the WNW at 12 mph. You can see that he has lost some of the convection that he had during the day and there still is no real obvious tight spin in Don. On the water vapor loop you can see that he is being sheared from the northeast and there is still is some dry air in front of Don.

The daytime heating of the Yucatan Peninsula may have caused some convective energy to be stolen from that area. But once he moves away from the landmass that wont hinder him any further. The only other factor is the vertical wind shear. From the shear tendency graph below you can see that there is only 5-10 knots of shear in his way, which is easily manageable. So with those factors Don should be able to slowly strengthen over the next 24-36 hours.

Model guidance for Don may change a little bit again in the morning once we get a good run that includes the recon data from earlier today. But for now they are pointing Don at the entire Texas coastline. The HWRF which has been steller on 48 hour track guidance over the past few years is leaning towards Corpus Christi and the GFDL is about 200 miles northeast near Galveston. In about 48 hours or so, on Friday night Don will likely make landfall on the Texas coast as a tropical storm. Don becoming a hurricane though cannot be ruled out just because the models are not taking him that strong. With the exception of the GFDL, they do take Don to the threshold of a Hurricane and he is in an area known for rapid intensification.

Elsewhere in the tropics there are 2 waves worth watching. You can see them on the surface vorticity map below. One is at the windward islands and could become our next invest, although there is no model support for this. (I've heard that before somewhere, lol). And a wave that came off of Africa yesterday that is now at 30w. That wave has received some attention from the global models for future consideration.

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