Wednesday, May 09, 2007

Subtropical storm: May 9, Update A

Good morning,

Our potential first named storm of the season is still loitering
mischievously off the S. Carolina/Georgia/Florida coast. All you
surfers... time to pop over to the east coast of Florida.

The NHC sent a reconnaissance plane in to investigate this morning. I
suspect they will give this one a name later today. It has wind speeds
in the lower end of the Tropical Storm range (34-63kt, 39-73mph), it has
a broad, not well-formed eye, and a pretty good circulation. In the
atmosphere, the wind shear is low, which is favorable for the storm.
However, it is almost completely surrounded by dry air, which is not so
favorable. In the ocean, it is hanging out over water temperatures of
about 24-25 degs C, which is lower than those needed for storm formation
(generally 26.5 deg C and above are the temperatures to keep an eye out
for - all puns always intended :) ). It has begun to interact with land,
which will also keep it from developing.

So... the question is that given all the conditions that would prevent a
storm from developing, why has this persisted? One reason is that it is
very slow moving and has basically remained over the Gulf Stream for
most of it's life. Although the surface waters of the Gulf Stream are
warmer than surrounding waters, the important factor is that the water
is warm here with depth as well, so the water that is being churned up
from beneath the surface of the ocean is as warm as the surface, not
colder as you might expect. The persistence (and weak strength) of this
storm has very little to do with actual surface temperatures and global
warming, and in that respect it is like many storms we have seen over
the past few years, and will probably see again this year. Another
reason is that it was formed as part of a frontal system in the
atmosphere, so it had a lot of energy (and water vapor) associated with
it to begin with as it developed into a non-tropical low pressure system.

I'll send out another note once I hear they have named it (or not).

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