Don holds on

Good evening everyone!

Don has hit a bit of a bump in the road tonight.  Its a bit tricky to pinpoint the exact reason for this, but I believe there are two minor causes: convergence aloft and a bit of an energy drain.  Before I get to that though, the 11pm advisory information is as follows:

  • Maximum sustained winds: 40 mph
  • Minimum Central Pressure: 1000 mb
  • Movement: WNW at 12 mph
  • 22.8N 88.1W
  • Tropical Storm Watches: From Port Mansfield to west of San Luis Pass, Texas
Looking into what happened since the last update, we have to first look at the latest satellite images: http://www.ssd.noaa.gov/goes/flt/t1/flash-rb.html . The scale goes from aqua to reds.  The aqua colors are warmer cloudtops and the reds are colder cloudtops which signify stronger storms.  You can see just from this satellite that the reds have turned into yellows, and therefore the storms inside of Don are a bit weaker than they were about 8pm or so. This is partially due to the Bermuda High building in to the northeast and moisture interruptions from the Yucatan.

Areas of high pressure are hills of air, and what goes up must come down especially in meteorology.  Air in the Bermuda High is constantly falling toward the surface of the Earth which is known as subsidence, and when it gets close enough to tropical cyclones it hinders their growth. Also called convergence aloft because air in the upper atmosphere comes together and can only come down often forcing thunderstorms to come down in intensity. You can see this happening on the northern side of TS Don.

Another story is unfolding on the southern and eastern sides of Don.  With the Yucatan peninsula just to the south of Don, the added energy from Don sent sea breeze storms up across the Yucatan.  This used up some of the moisture and energy that Don needs to convect thunderstorms and intensify.

As Don moves away from the hill of air and the Yucatan, conditions will improve.  This will happen overnight, and Don should be well on its way to intensification by the time recon gets to it tomorrow morning.  I think that Don may have briefly been at 45 mph a few hours ago, and I think that Don will get back to that intensity or better by the time recon gets in there.

I am sticking to my forecast of a maximum intensity of 60-70 mph until I see a decent strengthening trend if one does occur. Some of the guidance does take Don to category one hurricane strength before landfall on Friday, but with this recent bump I am cautious about bumping the intensity forecast up.  Below is my most recent forecast:

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Posted on Wednesday, July 27th, 2011, in Tropical Weather and tagged , , , . Bookmark the permalink. Leave a comment.

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