Monday, July 07, 2008

[Jyo_hurricane] Hurricane Bertha: July 7 update A

Great googliemooglies... I knew as soon as I called her 'Boring Bertha'
that she would start to change - it was like throwing down the gauntlet.

Although she is a hurricane (cat 1 wind range 74-95mph), she was barely
one when they upgraded her from a TS to a hurricane early this morning.
The wind speeds are calculated from satellite information, not from in
situ data within the system, so they are not very accurate. The discussion
from the NHS this morning says:


The Dvorak technique is used to estimate the wind speed from satellite
data. Although their calculations showed winds of slightly less than
hurricane strength, the images showed an eye so she was upgraded. I'll
ramble about the Dvorak technique in a later entry.

In this case we were all wrong - the NHS (and models) yesterday forecast
her to reach hurricane strength 24 hours from now (Tues am), and I did not
think she would quite make it and would remain a very strong TS.

She is now at about 19.5N, 50.5W and is moving in a W-NW direction at 17
mph. She will clear the Caribbean, but how far west she moves before
curving into the Atlantic is still debatable. The reason the system is
slowing in forward motion is because she is bumping up against that high
pressure - it's like anything moving up a hill, a bit slower depending on
how steep the gradient is.

There is a well-defined eye and she is looking good: Beautiful Bertha :)
The circulation is not very deep into the atmosphere, so although she
looks good, she is still a very weak cat 1.

She is almost completely surrounded by dry air, so the moisture is
predominanatly coming from evaporation from the ocean. Temperatures
underneath are 26-27 degs C, but within a few hours she will be over water
temperatures of 27-28 deg C, and given the slower forward motion and her
recent intensificaton, it looks likely that she will get stronger. The
wind shear is not very high this morning (except at the north-eastern edge
of the storm) and it does not look like it will get much stronger in the
next 24 hours. The NHS forecast keeps her as a cat 1 storm though.

In 1996 a previous incarnation of Bertha became a Hurricane on July 7.

More later today.

Blogs archived at:
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. If I "run
away, run away" (Monty Python), I'll let you know.

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