Saturday, September 16, 2006

Hurricane Gordon & Hurricane Helene: September 16, Update A

Hurricane Gordon:
Yes, he's still a hurricane... but barely. Winds are near 75mph (cat1:
74-95mph). As he has been pretty much stationary overnight, the decrease
in intensity has been slow. Once he starts moving (and it looks like he
has slowly started in a northward direction - or maybe in a slight
north-northwestward direction but that could be a wobble) then he will
cross into 25 deg C waters - he's not far from that region so the time
it takes will obviously really depend on how fast he gets going. For
those who don't know, stationary or stalling means that the storm is not
moving forward.

Why would a storm stall?
Well, tropical storms are generally steered by mid-to-upper level
(around 4km-13km above ground) pressure systems. The storm will move in
a clockwise direction around a high pressure system in the northern
hemisphere. This is what Gordon has been doing for most of his life -
imagine a clock face... he started off moving in the 6-9 quadrant (i.e.
west-northwest), and when he made that northeast turn, he began moving
in the 9-12 quadrant. Clockwise motion. But high pressure systems are
not as nice and round and solid as a clock face would be (otherwise that
would make this forecasting too easy and lots of people would be out of
a job :) ). These pressure systems evolve with time (hence the changes
in the forecast direction). A storm will stall if high pressure develops
in the path of a storm. I tell people it's like a ball (storm) trying to
roll up-hill. If it has room, it will adjust and try and move around
this by moving in a more westward direction (clockwise) until it gets to
an area it can cross. But if there is no room for movement, the system
will stop where it is. These pressure systems are also partly why storms
move forward at varying speeds.

The converse to the high pressure systems are the low pressure
systems... I'll get into that another day when there's a storm that will
provide an example.

Hurricane Helene:
He-storms and she-storms are created equal... well, at this point in
time and only as far as max. sustained winds go because Helene and
Gordon are, indeed, at the same strength. Helene's sustained winds are
near 75mph too, making her just about a hurricane. But unlike Gordon,
who has had his day, she will grow some more and get stronger. She's
already much bigger in area than Gordon is. She's moving along at a
respectable 14mph

Helene is in 27-28 degs C water and will continue over that for at least
another day. This means she will slowly intensify. She's in an
environment of low-to-moderate wind shear, coming out of the north-west.
Although the direction of wind shear will change in the next day or so,
it doesn't look like it will get any stronger. As I said the past couple
of days, there is dry air around this storm (to the west and north), but
it really it doesn't look like it is reaching the center and therefore
won't have as big an impact as it has for other storms.

I'm glad she's moving in a more northwestward direction than before. Now
I have more confidence that she will stay away from most land. Whether
or not she will clip Bermuda though is still a question (in my mind).

Today I expect some slow intensification of this system, but probably
still within the cat 1 range.

I'm only posting one entry today as nothing much is going on out there
(ha ha ha).
More tomorrow morning.
These remarks are just what I think/see regarding tropical storms (my
storm blog). If you are making an evacuation decision, please heed your
local emergency management and the National Hurricane Center's official
forecast. This is not an official forecast.

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