Hurricane Katrina

[x-y-no]

no Disc?

Discussion usually comes out a little later than the forecast and advisory.

[Brent]

TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT TUE AUG 23 2005

DATA FROM AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT...ALONG
WITH OBSERVATIONS FROM THE BAHAMAS AND NEARBY SHIPS...INDICATE THE
BROAD LOW PRESSURE AREA OVER THE SOUTHEASTERN BAHAMAS HAS BECOME
ORGANIZED ENOUGH TO BE CLASSIFIED AS TROPICAL DEPRESSION TWELVE.
THE INITIAL INTENSITY OF 30 KT IS BASED RECON WINDS OF 39 KT AT 800
FT...AND SHIP A8CI9 REPORTING 30-KT SUSTAINED WINDS AT 18Z IN THE
NORTHEAST QUADRANT. UPPER-LEVEL OUTFLOW IS WEAK...BUT IMPROVING AS
A SMALL ANTICYCLONE HAS BEEN DEVELOPING ABOVE THE LOW-LEVEL CENTER.

THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 310/07. THE LOW-LEVEL
CENTER HAS BEEN REFORMING WITHIN A LARGE CLEAR AREA NOTED IN
SATELLITE IMAGERY. HOWEVER...FLIGHT-LEVEL RECON WINDS CLEARLY
INDICATE A BROAD BUT OTHERWISE WELL-DEFINED LOW-LEVEL WIND FIELD.
THERE HAVE BEEN SEVERAL SMALL VORTICES DEVELOP WITHIN THE
CONVECTION IN THE EASTERN SEMICIRCLE AND THEN ROTATE WESTWARD OUT
FROM UNDER THE CONVECTION. THE INITIAL POSITION IS ROUGHLY THE
GEOMETRIC CENTER OF ALL THE SMALL SWIRLS...BUT SOME RE-ORGANIZATION
OF THE CENTER WITHIN THE CONVECTION IS POSSIBLE. TD-12 IS EXPECTED
TO CONTINUE MOVING SLOWLY NORTHWESTWARD TOWARD A WEAKNESS IN THE
MID-LEVEL SUBTROPICAL RIDGE. THIS WEAKNESS SHOWS UP BEST IN 500 MB
DATA...AND THEN DISAPPEARS BELOW AND ABOVE THAT LEVEL. BY 36-48
HOURS...ALL OF THE GLOBAL MODELS AND THE GFDL MODEL FORECAST THE
WEAKNESS TO FILL AND BE REPLACED BY A BROAD EAST-WEST ORIENTED
RIDGE. THIS SHOULD HELP TO DRIVE THE CYCLONE MORE WESTWARD ACROSS
SOUTHERN FLORIDA IN 60-72 HOURS...AND THEN INTO THE EASTERN GULF OF
MEXICO BY 96 HOURS. THIS SCENARIO IS CONSISTENT WITH THE NHC MODEL
CONSENSUS AND THE DEVELOPING SYNOPTIC PATTERN.

THE INTENSITY FORECAST IS A LITTLE TRICKY DUE TO THE UNCERTAINTY ON
EXACTLY WHEN A WELL-DEFINED CENTER WILL DEVELOP AND HOW SOON
CONVECTION WRAPS AROUND THE WEST SIDE OF THE CIRCULATION. THE
UPPER-LEVEL FLOW IS FORECAST TO REMAIN STRONGLY DIFLUENT FROM THE
NORTH FOR THE NEXT 24-36 HOURS...AND THEN BECOME NORTHEASTERLY TO
EASTERLY AFTER THAT. SINCE THE SHEAR IS ALSO FORECAST TO REMAIN
RELATIVELY LOW AT AROUND 10 KT AND SSTS WILL BE NEAR 31C UNDER THE
CENTER...AT LEAST STEADY INTENSIFICATION APPEARS TO BE IN ORDER. IF
CENTRAL CONVECTION DEVELOPS WITHIN THE NEXT 24 HOURS...THEN THIS
SYSTEM COULD REACH HURRICANE STRENGTH BEFORE IT MAKES LANDFALL. THE
OFFICIAL INTENSITY FORECAST IS SLIGHTLY LOWER THAN THE SHIPS MODEL.

THE NWS RULES GOVERNING THE NAMING OF TROPICAL CYCLONES SPECIFY
THAT...WITHIN A BASIN...WHEN A CYCLONE FORMS FROM THE REMNANT OF A
PREVIOUSLY EXISTING CYCLONE...THE OLD NAME/NUMBER IS RETAINED.
TROPICAL DEPRESSION TWELVE HAS A COMPLEX GENESIS THAT LIKELY
INCLUDES A MID-LEVEL REMNANT OF FORMER TROPICAL DEPRESSION TEN. A
REVIEW OF SATELLITE AND RAWINSONDE DATA OVER THE PAST WEEK OR SO
SUGGESTS THAT A SECOND DISTURBANCE APPROACHED AND COMBINED WITH THE
MID-LEVEL REMNANT OF TROPICAL DEPRESSION TEN ON 20 AUGUST. BECAUSE
IT IS IMPOSSIBLE TO DETERMINE WHICH OF THESE TWO SYSTEMS IS
ASSOCIATED WITH TODAY'S GENESIS...WE HAVE ELECTED TO USE THE
DESIGNATION TWELVE RATHER THAN TEN FOR THE NEW DEPRESSION. THIS
SITUATION DIFFERS FROM LAST YEAR'S REGENERATION OF IVAN...IN WHICH
THE LOW-LEVEL REMNANT OF THAT SYSTEM REMAINED A DISTINCT FEATURE
THAT COULD BE FOLLOWED CONTINUOUSLY UNTIL IT REGENERATED.

FORECASTER STEWART


FORECAST POSITIONS AND MAX WINDS

INITIAL 23/2100Z 23.2N 75.5W 30 KT
12HR VT 24/0600Z 24.0N 76.5W 35 KT
24HR VT 24/1800Z 25.0N 77.7W 40 KT
36HR VT 25/0600Z 25.7N 78.5W 45 KT
48HR VT 25/1800Z 26.0N 79.4W 60 KT
72HR VT 26/1800Z 26.3N 81.0W 50 KT...INLAND
96HR VT 27/1800Z 26.5N 83.5W 60 KT
120HR VT 28/1800Z 27.5N 86.0W 65 KT

[Brent]

Double. Ugh.

[HURAKAN]

Tropical Depression Twelve Discussion Number 1


Statement as of 5:00 PM EDT on August 23, 2005



data from an Air Force Reserve unit reconnaissance aircraft...along
with observations from the Bahamas and nearby SHIPS...indicate the
broad low pressure area over the southeastern Bahamas has become
organized enough to be classified as Tropical Depression Twelve.
The initial intensity of 30 kt is based recon winds of 39 kt at 800
ft...and ship a8ci9 reporting 30-kt sustained winds at 18z in the
northeast quadrant. Upper-level outflow is weak...but improving as
a small anticyclone has been developing above the low-level center.
The initial motion estimate is an uncertain 310/07. The low-level
center has been reforming within a large clear area noted in
satellite imagery. However...flight-level recon winds clearly
indicate a broad but otherwise well-defined low-level wind field.
There have been several small vortices develop within the
convection in the eastern semicircle and then rotate westward out
from under the convection. The initial position is roughly the
geometric center of all the small swirls...but some re-organization
of the center within the convection is possible. TD-12 is expected
to continue moving slowly northwestward toward a weakness in the
mid-level subtropical ridge. This weakness shows up best in 500 mb
data...and then disappears below and above that level. By 36-48
hours...all of the global models and the GFDL model forecast the
weakness to fill and be replaced by a broad east-west oriented
ridge. This should help to drive the cyclone more westward across
southern Florida in 60-72 hours...and then into the eastern Gulf of
Mexico by 96 hours. This scenario is consistent with the NHC model
consensus and the developing synoptic pattern.
The intensity forecast is a little tricky due to the uncertainty on
exactly when a well-defined center will develop and how soon
convection wraps around the west side of the circulation. The
upper-level flow is forecast to remain strongly difluent from the
north for the next 24-36 hours...and then become northeasterly to
easterly after that. Since the shear is also forecast to remain
relatively low at around 10 kt and SSTs will be near 31c under the
center...at least steady intensification appears to be in order. If
central convection develops within the next 24 hours...then this
system could reach hurricane strength before it makes landfall. The
official intensity forecast is slightly lower than the SHIPS model.

The NWS rules governing the naming of tropical cyclones specify
that...within a basin...when a cyclone forms from the remnant of a
previously existing cyclone...the old name/number is retained.
Tropical Depression Twelve has a complex genesis that likely
includes a mid-level remnant of former Tropical Depression Ten. A
review of satellite and rawinsonde data over the past week or so
suggests that a second disturbance approached and combined with the
mid-level remnant of Tropical Depression Ten on 20 August. Because
it is impossible to determine which of these two systems is
associated with today's genesis...we have elected to use the
designation twelve rather than ten for the new depression. This
situation differs from last year's regeneration of Ivan...in which
the low-level remnant of that system remained a distinct feature
that could be followed continuously until it regenerated.
Forecaster Stewart


forecast positions and Max winds

initial 23/2100z 23.2n 75.5w 30 kt
12hr VT 24/0600z 24.0n 76.5w 35 kt
24hr VT 24/1800z 25.0n 77.7w 40 kt
36hr VT 25/0600z 25.7n 78.5w 45 kt
48hr VT 25/1800z 26.0n 79.4w 60 kt
72hr VT 26/1800z 26.3n 81.0w 50 kt...inland
96hr VT 27/1800z 26.5n 83.5w 60 kt
120hr VT 28/1800z 27.5n 86.0w 65 kt

[HURAKAN]

Tropical Depression Twelve Discussion Number 1


Statement as of 5:00 PM EDT on August 23, 2005



data from an Air Force Reserve unit reconnaissance aircraft...along
with observations from the Bahamas and nearby SHIPS...indicate the
broad low pressure area over the southeastern Bahamas has become
organized enough to be classified as Tropical Depression Twelve.
The initial intensity of 30 kt is based recon winds of 39 kt at 800
ft...and ship a8ci9 reporting 30-kt sustained winds at 18z in the
northeast quadrant. Upper-level outflow is weak...but improving as
a small anticyclone has been developing above the low-level center.
The initial motion estimate is an uncertain 310/07. The low-level
center has been reforming within a large clear area noted in
satellite imagery. However...flight-level recon winds clearly
indicate a broad but otherwise well-defined low-level wind field.
There have been several small vortices develop within the
convection in the eastern semicircle and then rotate westward out
from under the convection. The initial position is roughly the
geometric center of all the small swirls...but some re-organization
of the center within the convection is possible. TD-12 is expected
to continue moving slowly northwestward toward a weakness in the
mid-level subtropical ridge. This weakness shows up best in 500 mb
data...and then disappears below and above that level. By 36-48
hours...all of the global models and the GFDL model forecast the
weakness to fill and be replaced by a broad east-west oriented
ridge. This should help to drive the cyclone more westward across
southern Florida in 60-72 hours...and then into the eastern Gulf of
Mexico by 96 hours. This scenario is consistent with the NHC model
consensus and the developing synoptic pattern.
The intensity forecast is a little tricky due to the uncertainty on
exactly when a well-defined center will develop and how soon
convection wraps around the west side of the circulation. The
upper-level flow is forecast to remain strongly difluent from the
north for the next 24-36 hours...and then become northeasterly to
easterly after that. Since the shear is also forecast to remain
relatively low at around 10 kt and SSTs will be near 31c under the
center...at least steady intensification appears to be in order. If
central convection develops within the next 24 hours...then this
system could reach hurricane strength before it makes landfall. The
official intensity forecast is slightly lower than the SHIPS model.

The NWS rules governing the naming of tropical cyclones specify
that...within a basin...when a cyclone forms from the remnant of a
previously existing cyclone...the old name/number is retained.
Tropical Depression Twelve has a complex genesis that likely
includes a mid-level remnant of former Tropical Depression Ten. A
review of satellite and rawinsonde data over the past week or so
suggests that a second disturbance approached and combined with the
mid-level remnant of Tropical Depression Ten on 20 August. Because
it is impossible to determine which of these two systems is
associated with today's genesis...we have elected to use the
designation twelve rather than ten for the new depression. This
situation differs from last year's regeneration of Ivan...in which
the low-level remnant of that system remained a distinct feature
that could be followed continuously until it regenerated.
Forecaster Stewart


forecast positions and Max winds

initial 23/2100z 23.2n 75.5w 30 kt
12hr VT 24/0600z 24.0n 76.5w 35 kt
24hr VT 24/1800z 25.0n 77.7w 40 kt
36hr VT 25/0600z 25.7n 78.5w 45 kt
48hr VT 25/1800z 26.0n 79.4w 60 kt
72hr VT 26/1800z 26.3n 81.0w 50 kt...inland
96hr VT 27/1800z 26.5n 83.5w 60 kt
120hr VT 28/1800z 27.5n 86.0w 65 kt

[gkrangers]

Great discussion....glad they included the discussion on the naming.

[chadtm80]

[Scorpion]

Gonna be an interesting next few days.

[sponger]

Good ole mcl! It held together all the way through. All you doubting thomas's need to have some faith!

[frederic79]

This would really apply more to a well developed storm with a strong central core, but given what's ahead, I find it very interesting that the primary conditions needed for extreme intensity are:

1- upper tropospheric anticyclone enhancing outflow (forecast to develop)
2- abundant cumulus convection (exists)
3- strong LLC (exists)
4- light or non-existent vertical wind sheer (10 knots)
5- SST's higher than 28.5 degree C (exists in abundance)
6- reasonable forward speed (8 mph is very reasonable)
7- warm, moist environment; absence of dry air (exists)

Hmmm...

[hurricanefreak1988]

Meanwhile, here in NC, we'll just sit back and watch, waiting for the newbie Lee to come. Looks like Katrina won't be The One.

[CaneCurious]

That is a VERY WIDE cone.

[DAVE440]

NHC is forecasting it to be a tropical storm by the time it gets here.

Any chance of it strenghtening more or just not enough time?

It's headed right for me so I'm not rootin for it...haha...
(then again...as already stated...it is a pretty wide cone)

Just wonderin....

Anyone remember the scene from Airplane with Lloyd bridges in the tower......? "It's headed right for us!!" as he jumps out the tower window...LOL!

[Marilyn]

Meanwhile, here in NC, we'll just sit back and watch, waiting for the newbie Lee to come. Looks like Katrina won't be The One.

Whats katrina going to do? be a fish. And Lee can just leave us alone too.

[Matt-hurricanewatcher]

katrina=Floridia. Lee maybe 97L then out to sea.

[Dean4Storms]

Does anyone detect a NW movement? Looks more like a 290-295 or more WNW to me. Although I admit it is really hard with the cirrus over the center, but overall it looks to be moving more WNW.


Also, the GFS keeps developing another wave and heading it for the islands by late next week, looks like things are going to get popping!

[Buck]

They seem to be taking their time with the 8pm Intermediate Advisory.

[dixiebreeze]

Tropical Depression Twelve Intermediate Advisory Number 1a


Statement as of 8:00 PM EDT on August 23, 2005



...Tropical depression moving slowly over the Bahamas...

a Tropical Storm Warning is in effect for the central and northwest
Bahamas...including Cat Island...the Exumas...Long Island...Rum
Cay...San Salvador...the northwestern Bahamas...the Abacos...Andros
Island...the Berry Islands...Bimini...Eleuthera...Grand Bahama
Island...and New Providence.

A tropical storm or Hurricane Watch may be required for portions of
southern Florida later tonight.

For storm information specific to your area...including possible
inland watches and warnings...please monitor products issued
by your local weather office.

At 8 PM EDT...0000z...the center of Tropical Depression Twelve was
estimated near latitude 23.3 north... longitude 75.8 west or about
160 miles... 255 km... southeast of Nassau.

The depression is moving erratically toward the west-northwest near
7 mph... 11 km/hr... and this general motion is expected to
continue for the next 24 hours.

Maximum sustained winds are near 35 mph... 55 km/hr... with higher
gusts. Some strengthening is forecast during the next 24 hours...
and the depression could become a tropical storm by Wednesday.

The estimated minimum central pressure is 1007 mb...29.74 inches.

Total rainfall accumulations of 3 to 6 inches are possible over
portions of the Bahamas...and along the northern coast of Cuba...
with isolated maximum amounts of 8 inches possible along the
northern coast of Cuba.

Storm surge flooding of 3 to 5 feet above normal tide levels...
along with large and dangerous battering waves...can be expected
near the center in areas of onshore winds in the Bahamas.

Repeating the 8 PM EDT position...23.3 N... 75.8 W. Movement
toward...west-northwest near 7 mph. Maximum sustained
winds... 35 mph. Minimum central pressure...1007 mb.

The next advisory will be issued by the National Hurricane Center at
11 PM EDT.

Forecaster Knabb

[mahicks]

Does anyone detect a NW movement? Looks more like a 290-295 or more WNW to me. Although I admit it is really hard with the cirrus over the center, but overall it looks to be moving more WNW.


Also, the GFS keeps developing another wave and heading it for the islands by late next week, looks like things are going to get popping!

Probably a wobble...
LOL...I always wanted to be the first to say that in a discussion!!!!!!!!!!!

[Coredesat]

TD12 has been wobbling a bit over the past couple hours, and the latest advisory takes that into consideration (and changes the direction to WNW).