ATL: ISAAC - Post-Tropical - Discussion

[canes04]

All systems go. He's ready for lift off.
I can imagine the local media in SFL must be in a frenzy.

[Bocadude85]

00
FXUS62 KMFL 211809
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
209 PM EDT TUE AUG 21 2012

.DISCUSSION...
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS
THE INTERIOR AND PUSH TOWARDS THE NORTHEAST SECTIONS OF THE CWA THIS
AFTERNOON AND INTO THE EVENING UNDER THE SOUTHWEST FLOW ALOFT. A
FEW STORMS COULD BE STRONG...WITH THE MAIN THREAT BEING STRONG
WINDS OF 40 TO 50 MPH. THE HRRR IS SHOWING THAT A LINE OF STORMS
MAY MOVE ACROSS THE EASTERN GULF AND INTO CENTRAL FLORIDA...WITH
THE TAIL END OF THIS LINE OF SHOWERS AND THUNDERSTORMS POSSIBLY
MOVING INTO THE LOCAL GULF WATERS AND PORTIONS OF THE NORTHWEST
AFTER 00Z. THIS IS CONSISTENT WITH THE 12Z GFS SHOWING A PIECE OF
ENERGY ROTATING AROUND THE BASE OF THE TROUGH AND ACROSS CENTRAL
FLORIDA OVERNIGHT. SO WILL KEEP 20-30 POPS FOR THIS REGION.

THE UPPER TROUGH ALONG THE EASTERN SEABOARD WILL BEGIN TO FILL AND
LIFT TO THE NORTHEAST TONIGHT AND WEDNESDAY...BUT A WEAKNESS WILL
REMAIN OVER THE GULF AND THE WESTERN ATLANTIC THROUGH THE WEEKEND.
AT THE SURFACE...THE QUASI-STATIONARY FRONT OVER NORTH FLORIDA
WILL SLOWLY DRIFT SOUTHWARD TONIGHT INTO WEDNESDAY AND THEN BEGIN
TO WASH OUT AND DRIFT NORTHWARD INTO THURSDAY. THE SUBTROPICAL
RIDGE OVER THE WESTERN ATLANTIC WILL MOVE NORTHWARD AND THE DRY
AIR AND HAZE OVER THE BAHAMAS IS EXPECTED TO PUSH INTO SOUTH
FLORIDA ON WEDNESDAY AND THURSDAY. IN ADDITION...THE LOW/MID LEVEL
FLOW WILL SHIFT FROM THE SOUTHWEST TO THE EAST AND SOUTHEAST BY
THURSDAY.

WITH PWATS FALLING TO AROUND 1.5 INCHES ON WEDNESDAY ALONG THE
SOUTHEAST COAST...ONLY MINIMAL RAIN CHANCES ARE EXPECTED.
STEERING FLOW WILL PUSH STORMS SLOWLY TO THE NORTH ON WEDNESDAY.
HIGHER MOISTURE WILL ALSO LINGER AROUND THE LAKE ON WEDNESDAY...SO
THERE WILL STILL BE A CHANCE OF STORMS FOR THE LAKE OKEECHOBEE
REGION. MODEL SOUNDINGS ARE SHOWING RELATIVELY STEEP LAPSE RATES
ABOVE THE INVERSION AND STRONG STORMS AND POSSIBLY AN ISOLATED
SEVERE STORM CANNOT BE RULED OUT ON WEDNESDAY. HEAT INDICES WILL
BE THE TYPICAL 100-108F FOR THIS TIME OF YEAR...WITH THE HIGHEST
READINGS ACROSS THE INTERIOR.

EVEN DRIER AIR IS EXPECTED TO MOVE INTO THE REGION ON
THURSDAY...WITH PWATS ACROSS THE REGION DROPPING TO 1.3-1.6 INCHES.
WITH THE FLOW SHIFTING TO THE EAST AND SOUTHEAST...EXPECT THE EAST
COAST TO MAINLY STAY DRY...WITH ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE INTERIOR AND TOWARDS THE GULF COAST.

FOR FRIDAY INTO SATURDAY...THE PRESSURE GRADIENT MAY BEGIN TO
TIGHTEN AS TROPICAL DEPRESSION NINE MOVES NEAR HAITI AND EASTERN
CUBA. SO SOMEWHAT BREEZIER EASTERLY FLOW COULD BEGIN ON FRIDAY AND
SATURDAY WITH AN INCREASE IN LOW LEVEL MOISTURE AND RAIN CHANCES.

IT IS STILL TOO EARLY TO DETERMINE THE IMPACTS OF TROPICAL
DEPRESSION NINE ON SOUTH FLORIDA OR THE SURROUNDING MARINE AREAS IN
THE LONG TERM. HOWEVER...THERE IS INCREASING POTENTIAL THAT SOUTH
FLORIDA AND/OR THE SURROUNDING MARINE AREAS COULD BE IMPACTED LATE
THIS WEEKEND INTO EARLY NEXT WEEK. SO NOW IS A GOOD TIME TO
REVIEW INDIVIDUAL TROPICAL CYCLONE PREPAREDNESS PLANS. FOR THE
LATEST INFORMATION REGARDING TROPICAL DEPRESSION NINE...CONTINUE
TO MONITOR THE LATEST FORECASTS FROM THE NATIONAL HURRICANE
CENTER.

&&

[wxman57]

Maybe a wobble, but that LLC is moving WNW to NW?
http://www.ssd.noaa.gov/PS/TROP/floater ... -long.html

yup that's what wxman was talking about a bit earlier......and if that's not a wobble....man that is some illusion!

its only in response to each burst of convection pulling the center. it is not a change in general direction. besides that convection should begin to really come back over the next couple hours.

Yes, trochoidal motion (wobbling) due to convective bursts around the center. It's moving west though the center jumped around a bit for a while.

[SouthFLTropics]

All systems go. He's ready for lift off.
I can imagine the local media in SFL must be in a frenzy.

I don't even have to see the TV to know exactly what the 5:00PM broadcasts will lead with...(Cue dramatic music and caption "TROUBLE IN THE TROPICS"). Every person who's never been through a storm before will be running rampant with panic tomorrow morning and clearing off the shelves at Publix after the media whips them into a frenzy.

SFT

[Bocadude85]

All systems go. He's ready for lift off.
I can imagine the local media in SFL must be in a frenzy.

I don't even have to see the TV to know exactly what the 5:00PM broadcasts will lead with...(Cue dramatic music and caption "TROUBLE IN THE TROPICS"). Every person who's never been through a storm before will be running rampant with panic tomorrow morning and clearing off the shelves at Publix after the media whips them into a frenzy.

SFT

Lol yea and chances are that all the hype will be for nothing.

[SeminoleWind]

All systems go. He's ready for lift off.
I can imagine the local media in SFL must be in a frenzy.

I don't even have to see the TV to know exactly what the 5:00PM broadcasts will lead with...(Cue dramatic music and caption "TROUBLE IN THE TROPICS"). Every person who's never been through a storm before will be running rampant with panic tomorrow morning and clearing off the shelves at Publix after the media whips them into a frenzy.

SFT

it will be the same here in Central Florida as well, weather guys with there jackets off and sleeves rolled up and there in house model coming up later in the broadcast, lol.

[Weatherboy1]

Looks to be revving up with the convection again, and right over the LLC, at this time. If that can persist overnight, I wouldn't be surprised if we were dealing with a 50 mph wind storm by morning or so.

Just my opinion ... as always!

[wxman76]

Well you are right they are primitive equation models not specifically baroclinic or barotropic but one of the assumptions often used in these models to make the governing equations simpler to solve is to assume the atmosphere is barotropic. At least that was the case with the NGM and MRF when I was in school. And of course each model has it's own physics package to handle different situations which is probably a good thesis paper.

Speed and intensity aren't directly proportional. Yes a slower moving storm has a better chance to strengthen rapidly as it does not outrun it's convection. but you can have a strong storm move very fast or very slow. Same is true of a weak storm zipping along or just sitting there. What is more important about speed is timing with fronts. If isaac remains fast it will intersect the trough farther west and turn farther west. If it is slower the intersection is farther east.

Shear also affect the storm as it has isaac so far, but this should be dissipating. Remember the atmosphere around a storm controls it's movement not the storm itself. but it's like a cork in the stream. if you put a small cork in the stream it floats along bouncing like a bouy. If you throw a large ball in the stream there is more surface area to push against and it moves faster plus it can sample more of the stream being affected by currents that the small cork may not feel. Isaac has such a large envelope it should feel more than a small compact storm. hence the correction for storm strength in this case. But then again like all rules in meteorology they don't always apply the same. Every situation is different, every initial condition is different and every outcome is different.

There is another reason I like a farther East storm. For some reason the GFS likes to hit the pattern in the super long range. In this case when Isaac was in the long range it had it up the coast. in the middle range the GFS loves to lose it's idea, only to come back in the short range to it's original idea. This is why the ECMWF is usually a far superior model, especially when multiple jets are involved, split flow that sort of thing. The reason I don;t believe the 12z ECMWF is i feel this will be a stronger storm than progged. In fact the latest recon at 1004 mb is much lower than the 24 hr ECMWF at a sub 1012 mb storm. maybe it weakens but I'm hedging it doesn't.

This post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

[SouthFLTropics]

Maybe it's just me but it looks like TD-9 is slowing down some...Maybe that is why the convection is starting to pop around the LLC again.

SFT

[Shuriken]

I did not refer to any cap "above 200mb" or specify the tropopause inversion; the cap ("King") in question is the one which inhibits convection from reaching and exhausting at 200mb (i.e., that which keeps cloud tops generally lower and warmer, rather than, say, -75C). Depending upon the location and time of season, the actual height of this cap could widely vary.

The inability to exhaust above the tops of nearby convection, or the layer of subsidence generated by ITCZ/South American equatorial blow-off, will prevent a tropical system from intensifying.

TD9 is demonstrating the dominance of this factor today: last night, the cap loosened, and a big meatball blew up; this morning, well before the diurnal minima, the cap re-asserted itself and convection waned considerably to the point that the LLC is now exposed.

-- Why did this happen? Most people will fret over various surface factors such as dry air and so on; and much head-scratching ensues as systems inexplicably croak despite entering areas of better surface conditions for intensification.

I believe it's an entirely high altitude phenomena caused by gravity waves and similar perturbations along the tropopause which upset stability variables. Since these triggering phenomena are mainly invisible, there is an unconscious tendency to assume they do not exist, or at least not pay them due mind. (There have been scattered studies of high altitude import, but not enough for a general knowledge to percolate throughout the community of tropical devotees.)

Then I must confess as to not having any idea what you are referring to. Can you point to a study that discusses this capping layer around 200 mb, distinct from the tropopause (which does indeed usually exist higher up than 200 mb in the tropics)? If it exists, it can't have gone unnoticed. The lapse rates near 200 mb do change quite a bit due to effects from antecedent convection, etc., and this of course can have an impact on subsequent deep convection. Earlier in this thread, however, you made the following claim "I say: this is all about lapse rates to 200mb. As in: it is the determinant factor necessary for intensification of any tropical system up through Hurr to Major." That's a pretty strong claim, and I don't know of any tropical meteorologist who would agree with it. There really is no single determining factor, but rather many different ones from the sea surface temperatures to the environmental relative humidity through a deep layer, to the tropospheric lapse rates, to deep-layer wind shear that all contribute, and some are more dominant than others in different situations. If there were one determining factor, TC forecasting (especially of intensity) wouldn't be so darn difficult.

I welcome a theory which can rationally explain what else could result in, say, convection in nearly all parts of Ernesto puffing up simultaneously while in the southwestern Caribbean (I remember this quite distinctly) at one point, only to then stall after several more sat-frames. It was a very weird phenomena, but not necessarily one you'd pay attention to if you weren't actively looking for it. Dry air, shear and water temps varied throughout the system, and could not reasonably be the cause of such system-wide simultaneous behavior on a per sub-hour basis. (I've previously discounted diurnals in this particular Ernesto example, because it occurred at the wrong time of day).

Here's another example of the same phenomena with TD9 today: note re-energized convection sprouting simultaneously in all parts of the storm.

On a more general note, there are numerous reasons why these convective bursts in developing TCs might be inhibited, and surface conditions are only one factor. Your posts make it sound like the tropical meteorology community only pays attention to surface conditions. They don't. There are numerous studies on the effects of gravity waves on convection/etc, much more than "scattered".

I wrote: "(There have been scattered studies of high altitude import, but not enough for a general knowledge to percolate throughout the community of tropical devotees.) "

...given that I almost never see it discussed within these forums, I'll stand by that statement.

[JPmia]

All systems go. He's ready for lift off.
I can imagine the local media in SFL must be in a frenzy.

I don't even have to see the TV to know exactly what the 5:00PM broadcasts will lead with...(Cue dramatic music and caption "TROUBLE IN THE TROPICS"). Every person who's never been through a storm before will be running rampant with panic tomorrow morning and clearing off the shelves at Publix after the media whips them into a frenzy.

SFT

Yes and then add in the 20th anniversary of Hurricane Andrew and you've got a perfect recipe for hype and hyperbole.

[wxman57]

Maybe it's just me but it looks like TD-9 is slowing down some...Maybe that is why the convection is starting to pop around the LLC again.

SFT

It definitely slowed down today.

[Sanibel]

IMO, the wobbles connote a weakness that will result in recurvature. If it was under a strong ridge into Central America it wouldn't wobble at such a weak strength. Look out.


The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[Gustywind]

The Martinique yellow cyclone alert

franceantilles.fr 21.08.2012

http://www.microsofttranslator.com/bv.a ... 170695.php

The island has tilted in yellow vigilance this Tuesday afternoon after the depression tropical number 9, which the centre should pass near Guadeloupe Wednesday evening. Heavy rains expected in Martinique.

Martinique is yellow vigilance Cyclone since the Tuesday noon. Weather-France, time should remain relatively calm until end of the next night. But "an evolution of tropical storm depression in 24 hours". The most likely path at this point, the centre should pass near Guadeloupe Wednesday evening.
In this hypothesis, Martinique will be especially concerned with coming rains at the end of next night. "They will intensify the next night and will continue Thursday: important rollups are expected", still provides weather France.
The strong winds, which deploy North of the disturbance, should not concern us but strong gusts could accompany squall lines.
On Wednesday, the sea should gradually widen with average trough between 2 m 50 and 3 m.
Vigilance is recommended.

[BoudreauxWPB]

All systems go. He's ready for lift off.
I can imagine the local media in SFL must be in a frenzy.

I don't even have to see the TV to know exactly what the 5:00PM broadcasts will lead with...(Cue dramatic music and caption "TROUBLE IN THE TROPICS"). Every person who's never been through a storm before will be running rampant with panic tomorrow morning and clearing off the shelves at Publix after the media whips them into a frenzy.

SFT

That's why I went yesterday.

I'm waiting for the 5PM news to see exactly how they play it since the 5PM forecast will be out soon. As my offices' novice no nothing hurricane expert simply because I frequent this site but offer no useful information, co-workers have been in early panic mode all day simply because I mentioned a possible threat late this weekend to early next week.

[Bocadude85]

000
WTNT34 KNHC 212050
TCPAT4

BULLETIN
TROPICAL STORM ISAAC ADVISORY NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
500 PM AST TUE AUG 21 2012

...AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT FINDS THAT THE
DEPRESSION HAS BECOME A TROPICAL STORM...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...15.4N 53.9W
ABOUT 500 MI...810 KM E OF GUADELOUPE
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES

[WeatherGuesser]

Officially Isaac per NHC

[adam0983]

Isacc is born at 453pm.

[SouthFLTropics]

The 5:00PM discussion is out and based on reading it the NHC isn't biting into the EURO's big westward swing just yet. Doesn't surprise me since they aren't ones to make dramatic shifts one way or another, especially in the 5 day range.

SFT

[SeminoleWind]

The 5:00PM discussion is out and based on reading it the NHC isn't biting into the EURO's big westward swing just yet. Doesn't surprise me since they aren't ones to make dramatic shifts one way or another, especially in the 5 day range.

SFT

Good call for now Isaac is slowing and strengthening at least in the short term, something the Euro was slower to show