Tuesday, August 14, 2007

[Jyo_hurricane] TD 4: August 14, Update A

TD 4 is still just a Tropical Depression, and I don't see it changing
too much today, although the official forecast calls for it to become a
TS today (it called for it to become a TS yesterday too, which seemed
unlikely because of the wind shear). I believe it would be TS Dean next.

It is still in a region of decent wind shear, the water temperature is
around 27 degs C. It is difficult to pinpoint the exact center of
rotation because it is not a well formed storm, but I think that the
center might be south of the track currently indicated by the NHC. The
main convection is still to the east of the center of rotation. On its
current path I don't see it getting over warmer temperatures for at
least another day (and maybe two) - unless it moves southward. The
clouds tops have become warmer in the past couple of hours which is
typical of a weaker storm, but is probably a cycle the storm is going
through. If you look at the color Infra-red satellite image (e.g.

http://www.ssd.noaa.gov/goes/east/catl/avn-l.jpg) the colors will
indicate how high the cloud tops are. Red is colder and blue is warmer
(of course! ;) )

What is the significance of warmer cloud tops?
The atmosphere is divided into layers, and each layer is defined by the
temperature. In the layer closest to the earth (called the troposphere)
the temperature gets colder the higher up you go. In the next layer up
(the stratosphere) the temperature gets warmer the higher up you go, the
layer above that it gets colder and so on. The lowest layer (the
troposphere) extends from the earth's surface to between approximately
8-16km in altitude (generally speaking, 8km is near the polar regions,
16km is near the equatorial regions). Because of the large amounts of
convection associated with tropical storms, the clouds extend up in the
troposphere. The higher up in the troposphere the cloud tops are, the
colder they will be. A really strong tropical storm (hurricane) has
cloud tops that can extend to the tropopause (the boundary between the
troposphere and stratosphere).

More later,

These remarks are just what I think/see regarding tropical storms - not
the opinion of any organization I represent. If you are making an
evacuation decision, please heed your local emergency management and the
National Hurricane Center's official forecast and the National Weather
Service announcements. This is not an official forecast.

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