31 August 2004

Gaston submerges Richmond, Hermine makes landfall as a late summer night zephyr, and Frances stronger, faster (again)...

From Jonathan Vigh: 
Tropical Depression Gaston, already a prolific rain producer, went out with
a bang last evening. As the storm ciruculation slowly pinwheeled across
southeast Virginia, a massive convective blowup developed on the
circulation's northwest side. The resulting cloudburst dropped up to 4.5" of
rain in an hour over and near downtown Richmond, VA. A total of 5-12" fell
in just several hours across the city. The resulting flood turned downtown
Richmond into a raging, muddy rapids. Hundreds of cars floated away and a
20-block district of the city was submerged. Unfortunately, at least 5
people were killed. As the system moved on, a ship in the Chesapeake Bay
reported tropical storm force winds and the system was upgraded back to a
tropical storm. 

Meanwhile, the detached low level circulation of Hermine was racing
northward toward Massachussetts. Hermine made landfall at about 2 AM this
morning, bringing only some 20-25 kt southerly breezes into the area and
some thunderstorms. This was a much less significant event than the cold
front and storms which had drenched parts of New York and Vermont earlier. 

This afternoon, Tropical Storm Gaston moved passed Nantucket. It's
circulation is much more substantial than Hermine, but the storm is mainly a
marine interest. Most of the rain has finally ended across New England and
Gaston is headed for Nova Scotia and beyond, and will likely soon become

Hurricane Frances passed just 145 miles of San Juan, Puerto Rico this
afternoon. The storm passed the Leeward Islands overnight, but there were
few if any reports of tropical storm force winds. Saint Thomas reported a
gust to 32 kt as the outer rainbands passed by, and Puerto Rico is
experiencing similar conditions. The latest recon aircraft reported an
spectacular stadium effect in Frances' 26 nm diameter eye and an
extrapolated a central pressure of 938 mb. The eye is getting warmer with
time, a sign that usually points to more strengthening, or at the very
least, a mature hurricane. Frances underwent at least one eyewall cycle in
the last day, and overnight, the inner eye disintegrated, leaving the
current eye which has since contracted from 35 nm to 26 nm. The appearance
on satellite imagery is nothing short of awesome. Mesovortices have been
seen whipping around in the lower part of the eye. Frances looks a lot like
Isabel in some regards, but is not as strong . . . yet. For comparison, here
is a list of the Atlantic hurricanes over the past 5 years which reached a
peak intensity equal to or higher than Frances' current intensity (this is
in no way exhaustive or even guaranteed to be accurate):

2004 Frances(so far) 120 kt 938 mb
2004  Charley  125 kt 941 mb
2003  Isabel  145 kt 915 mb (est.)
2003 Fabian  125 kt 939 mb
2002 Lili  120 kt 940 mb
2001  Michelle 120 kt 934 mb
2001 Iris  125 kt 948 mb
2000 Keith  120 kt 941 mb
2000  Isaac  120 kt 943 mb
1999 Lenny  130 kt 933 mb
1999 Gert  130 kt 930 mb
1999  Floyd  135 kt 921 mb
1999 Cindy  125 kt 942 mb
1999 Bret  125 kt 944 mb

In summary, over 5 seasons (not counting 2004), there were 12 hurricanes
that were at least as strong as Frances (this is well above the long-term
average), an average of more than 2 per year. Only 4 storms reached 130 kt
and above -- storms this strong are pretty rare. Frances may reach this
level in the next day or two, as there are few negative factors to prevent
further strengthening. An upper low is spinning to the west over the Bahamas
-- this could crimp Frances outflow and even shear the system in a couple
days. It is more likely that Frances will nudge this system and interact a
bit, but probably not enough to cause substantial weakening. Frances'
strongest inhibition to further intensification might be internal dynamics
(eyewall cycles), but the storm is just as likely to strengthen as weaken in
that regard. Regardless of the exact strength, a severe hurricane is headed
towards the U.S. East Coast and is not likely to weaken to anything less
than a major hurricane. Potential landfall could be as soon as 4 days from
now (Saturday) or possibly as late as Sunday or early Monday. It is still
not possible to pinpoint the landfall location (or even the state of
landfall!), but the general risk area stretches all the way from Key West to
Cape Hattaras. Right now, the middle of that area, stretching from West Palm
Beach, FL to Brunswick, GA, probably has the highest chance of seeing the
major effects from Frances. Parts of the Bahamas will likely be hit
beforehand, and are currently under Hurricane Watches and Warnings.    

At 21Z, Frances was at 20.5N 65.9W and moving a little faster towards the
west at 15 kt with maximum sustained winds of 120 kt. 

Please visit my tropical Atlantic headquarters.

No comments:

Post a Comment