Tuesday, December 11, 2007

[Jyo_hurricane] Subtropical Storm Olga: December 11, Update A

STS Olga made landfall in the Dominican Republic this afternoon, and is
now inland. This should knock some steam out of her (all puns fully
intended). :)

As I thought yesterday, she has been moving in a little more northerly
direction than was predicted when I sent the last entry out. The track now
takes her north of Jamiaca instead of south. I still think this is a
little too far south, and am expecting a continuation of her current
west-northwest movement, bringing her closer to Cuba - which may not be a
problem because she may not be in good shape after crossing Hispaniola.

She's still a weak system (sustained winds of 45mph), and I agree with the
NHC - clearly not much room for intensification. She is, primarily, a rain
event not a wind event.

The VIs are almost clear of precipitation from this system, but PR is
still getting rain, as is the Domincan Republic and Haiti - so the
possibility of mudslides is there.

I did blog about Tropical vs. Subtropical vs. Extratropical storms a few
months ago (on June 1). I've cut and paste below what I wrote then - and
please feel free to send me more questions on this or any other aspect of
these storms. I should point out that a long time ago (around 2002), when
meteorologists were er... meteorologists :), subtropical storms were not
named storms and were, therefore, more clearly recognized as different

>From June 1 entry:

What is the difference between an extratropical storm, a tropical storm,
and a subtropical storm?

An Extratropical Storm: These usually form in the extratropics (quelle
suprise!) and have cold air at their core. A cold air mass meets a warm
air mass, and as the warm air rises (because it is lighter than the cold
air), it releases potential energy that results in these systems. Because
warm air rises, a low pressure is formed which is why these are also
called low pressure systems.They are usually associated with fronts which
are depicted on weather maps as lines of blue triangles (for a cold front)
or red semi-circles (for a warm front). Because it's the collision of air
masses, these systems can occur over land or water, and occur frequently
in the winter in the US as snowstorms/blizzards or Nor'easters.

A Tropical Storm: These usually form in the tropics (aren't we good at
naming things?) and have warm air at their core. The energy source for
these differ from extratropical storms. These storms form over water only
and the energy source is latent heat. Warm water evaporates into the air.
As the rising warm moisture-laden air in the center reaches colder
altitudes in the atmosphere, the water vapor condenses to form clouds and
latent heat is released. The heaviest rains and winds are in a band close
to the center. No fronts are associated with these storms (although
'waves' in the atmosphere are) - which makes it difficult to determine too
far ahead of time when a storm will develop. A tropical storm is when the
winds are greater than 34 knots (39 miles per hour). If the winds are less
than that, it is a tropical depression.

A Subtropical Storm: These usually contain some characteristics of both
extratropical and tropical systems. For example, imagine an extratropical
storm moving over warmer water. Now the storm begins to get some energy
from latent heat as well, and the cold air in the center (near the
surface) is replaced by warm air, so the storm core can change from cold
to warm. The heaviest rains and winds are not near the center. Like a
tropical system, a subtropical storm is when the winds are greater than 34
knots (39 miles per hour). If the winds are less than that, it is a
subtropical depression. Subtropical Storm Andrea was formed from an
extratropical low pressure system/front that moved eastward off the coast
of the US over warmer waters.

It's only since 2002 that subtropical storms were given names from the
hurricane name list - which would partly account for why we have had more
named storms in the past few years.

That's all for now folks. Have a lovely day!

Blogs archived at: http://www.jyotikastorms.blogspot.com/
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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