Tuesday, November 10, 2009

Extratropical Storm Ida: November 10 Update A

Ida made landfall earlier today as a weak Tropical Storm with winds of
about 50 mph, and very little convection. She then merged with that front,
and is now an extratropical system. This is my last entry on this system.

In response to a question I had asking what extratropical systems were, I
cut and paste this from an entry I wrote over two year ago. Boy was I
clever back then! What happened? (no need to answer that) ;-)

A quick overview of storm systems- 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.

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!
Toodle pip until the next time.


Updates archived at: jyotikastorms@blogspot.com

DISCLAIMER: You all know this already. My views, heed those who know, yada
yada yada...

No comments: