ATL: SANDY - Remnants - Discussion

[Caribwxgirl]

Ugh! The GFS ensemble have Jamaica squarely in their sight if this develops!

[Aric Dunn]

You have to watch out for these October western carrib systems models are known for greatly underestimating intensity in this area and the possibility of RI.

[wxman57]

No sign of any LLC yet. Probably late tomorrow or on Tuesday.

[jinftl]

Crownweather Discussion this morning:


Invest 99L Located In The Central Caribbean Likely To Become Tropical Storm & Possibly Hurricane Sandy This Week; Jamaica, Eastern Cuba, Hispaniola, The Bahamas & Possibly South Florida May Be Impacted By 99L/Sandy

Sunday, October 21, 2012 8:51 am
by Rob Lightbown

Invest 99L, which is an area of low pressure located over the central Caribbean is gradually becoming better organized this morning. Satellite loops this morning showed a definite increase in thunderstorm activity, especially on the eastern side of the low pressure system. Based on this and the fact that 99L is in a environment that is favorable for development, I think that this system will become a tropical depression by late tonight or Monday morning and then Tropical Storm Sandy by Monday evening or at the very latest Tuesday morning.

The various forecast guidance has shifted considerably further west in the forecast track of Sandy, especially once it gets north of Haiti and Cuba. It seems that the guidance is trending towards the Canadian model and this is potentially not so good news for the Bahamas, south Florida and potentially coastal sections of the southeastern US, Mid-Atlantic states and the northeastern US. Let’s take a quick look at each of the latest model guidance members:

The GFS model forecasts that Sandy to be to track over Jamaica on Wednesday, eastern Cuba on Thursday and then across the central and northwestern Bahamas on Friday coming quite close to southeastern Florida by Friday evening. From there, the GFS model forecasts that Sandy will phase with a strong trough of low pressure moving into New England on Sunday which if this verifies would bring very heavy rainfall and strong winds to much of New England on Sunday.

The European model forecasts that Sandy-to-be will track over Jamaica on Wednesday, eastern Cuba on Thursday and then across the central Bahamas on Friday and the northwestern Bahamas on Saturday. The European model does not phase Sandy with the eastward moving trough, but instead pulls it eastward out to near Bermuda by next Tuesday.

The Canadian model is the extreme of all of the model guidance in its phasing forecast. The Canadian model forecasts that Sandy will track just west of Jamaica on Thursday morning and then forecasts an extremely close brush if not landfall on southeastern Florida on Friday. The Canadian model also forecasts Sandy to phase with the eastward moving trough and become an extremely intense storm (central pressure of 962 millibars) near Virginia Beach by next Sunday morning.

It’s interesting to note that the UKMET model also hints at a track that is very similar to the Canadian model and shows it just west of Jamaica on Wednesday evening and then near the southern end of Andros Island in the Bahamas by Thursday evening.

So, here are my thoughts:
As I have really mentioned, I do think that 99L will be named Sandy by Tuesday at the very latest and a track north-northeastward right across Jamaica as a moderately strong tropical storm seems likely right now. The timeframe for this would be Wednesday evening. From there, Sandy may turn more northward and it “feels” the trough of low pressure to its west and starts to get captured by that trough. This means a track across the central/northwestern Bahamas is possible from near the southern end of Andros Island to right across Great Abaco Island on Thursday night or Friday morning. Now, a caveat here: A track further west very near southeastern Florida on Friday morning is certainly possible and this is something that will need to be watched for very closely.

Beyond that, I have concerns that the forecast guidance are trending towards the idea of Sandy phasing into the eastern trough of low pressure and potentially becoming an intense coastal storm for the Mid-Atlantic states and New England. At this point, it is a possibility and we have more than enough time to watch for this potential.

One final thought: Late season tropical storms and hurricanes in the Caribbean can be extremely fickle and difficult to forecast. If we take a look at climatology for Caribbean storms in late October, they tend to take a north-northwesterly track towards south Florida. Additionally, late season storms are notorious slow moving systems and do not escape out the Caribbean very quickly; so, it is plausible that the global models may be overdoing the track out of the Caribbean with this system. So, nothing is written in stone when it comes to 99L/Sandy and this is a system that bears very close scrutiny.

One thing that is for sure: 99L/Sandy is likely to bring heavy rainfall and life-threatening flash flooding and mudslides to Jamaica, eastern Cuba and Hispaniola for much of this week.

[gatorcane]

Interesting indeed. Out of town at the moment. Should be back online later this evening to check things out.

[cycloneye]

Sunday's discussion of 99L by Dr Jeff Masters:



A tropical wave embedded in a large trough of low pressure (Invest 99L) covers a large portion of the Central Caribbean between Hispaniola and the northern coast of South America. This storm has the potential to be a dangerous rainfall threat for Haiti, Jamaica, and eastern Cuba. The disturbance is headed west at less than 5 mph, is over very warm waters of 29°C, and is in a moist environment. 99L has a large area of heavy thunderstorms that have a good degree of spin. These thunderstorms are beginning to organize into spiral bands, as seen on visible satellite loops. However, the amount of heavy thunderstorm activity is about the same as yesterday, and there are no signs of a surface circulation. An Air Force hurricane hunter aircraft is scheduled to investigate 99L this afternoon, but I expect this flight will be rescheduled for later.


Forecast for 99L

Wind shear is a low 5 - 10 knots, and is forecast to be in the low to moderate range, 5 - 20 knots, through Tuesday. This should allow for some steady development of 99L, and there has been a good deal of model support for 99L becoming a tropical depression by Wednesday. Steering currents favor a continued slow westward movement for 99L through Tuesday. On Wednesday, a strong trough of low pressure to the north of 99L is expected to turn the storm to the north or north-northeast, which should put 99L in the vicinity of Jamaica on Wednesday and Eastern Cuba on Thursday. By Friday, 99L should be in the Central or Eastern Bahamas. It is unclear at this point whether or not the trough pulling 99L to the north will be strong enough to pull the storm all the way out to sea to the northeast; a narrow ridge of high pressure has the potential to build in over 99L late this week and force the storm west-northwest, with a potential threat to the western Bahamas and U.S. East Coast by next weekend. In their 8 am EDT tropical weather outlook, NHC gave 99L a 70% chance of developing into a tropical cyclone by Tuesday morning. 99L will be capable of bringing heavy rains of 5 - 10 inches, with isolated amounts of up to 15 inches in mountainous areas, to Jamaica and Haiti, Monday through Wednesday. Heavy rains will begin on Tuesday in Eastern Cuba, and spread northwards into the Central and Eastern Bahamas by Wednesday.

[SFLcane]

Excerpt From masters post this morning...

A narrow ridge of high pressure has the potential to build in over 99L late this week and force the storm west-northwest, with a potential threat to the western Bahamas and U.S. East Coast by next weekend.

[Caribwxgirl]

It's odd that when this was in talking tropics it had much more interest than is being shown now that its actually developing. Weird!

[cycloneye]

12z Surface Analysis. Look at the red arrow and see in which direction it will move in the next 24 hours.

[Caribwxgirl]

Ok that's going sw what does that mean potential track wise?

[jinftl]

Without any system potentially effecting south florida directly, the pressure gradient alone is going to bring very wind conditions our way late in the week....NWS Miami forecast for Miami Beach shows sustained winds around 30 mph gusting to 40 mph most of Friday.

http://forecast.weather.gov/MapClick.ph ... adDay.y=13

[cycloneye]

Ok that's going sw what does that mean potential track wise?

According to the synoptic pattern shown by the models,it moves WSW and then stops,then resumes a WNW, NW and then North to NNE motion. But is an enigma what track it will make as steering currents are weak on this time of the season.

[Caribwxgirl]

Ok that's going sw what does that mean potential track wise?

According to the synoptic pattern shown by the models,it moves WSW and then stops,then resumes a WNW, NW and then North to NNE motion. But is an enigma what track it will make as steering currents are weak on this time of the season.

I wish it would develop a coc so at least we'd be better able to predict movement. Also I'm not loving this slow crawl not a good thing at.

[Aric Dunn]

low level cloud pattern is pointing to increased organization. with low level curvature developing to the wet of all the convection but that should change soon as convection should build as the low level convergence increases so this time tomorrow we should have closed llc.

viewtopic.php?f=59&t=114017&start=60

[Aric Dunn]

low level cloud pattern is pointing to increased organization. with low level curvature developing to the wet of all the convection but that should change soon as convection should build as the low level convergence increases so this time tomorrow we should have closed llc or maybe even later tonight.

viewtopic.php?f=59&t=114017&start=60

[cycloneye]

It's odd that when this was in talking tropics it had much more interest than is being shown now that its actually developing. Weird!

You are right. However,watch as time goes by and the system starts to develop and the model trend to the west and more closer to the U.S continues,folks will flock to this thread.

[GCANE]

Now have a warm core

1C at 12km

http://rammb.cira.colostate.edu/product ... 3_TANO.GIF

[cycloneye]

Remains at 70%.



A BROAD AREA OF LOW PRESSURE...ASSOCIATED WITH A TROPICAL WAVE...IS
PRODUCING A LARGE AREA OF SHOWERS AND THUNDERSTORMS OVER THE
CENTRAL CARIBBEAN SEA. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE
CONDUCIVE FOR THE FORMATION OF A TROPICAL DEPRESSION DURING THE
NEXT COUPLE OF DAYS...AND THIS SYSTEM HAS A HIGH CHANCE...70
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS
AS IT MOVES SLOWLY WESTWARD AND BECOMES NEARLY STATIONARY WELL
SOUTH OF JAMAICA. HEAVY RAINS FROM THIS DISTURBANCE ARE LIKELY TO
SPREAD OVER JAMAICA...HISPANIOLA...AND EASTERN CUBA OVER THE NEXT
SEVERAL DAYS. THESE RAINS COULD PRODUCE LIFE-THREATENING FLASH
FLOODS AND MUD SLIDES...ESPECIALLY IN AREAS OF HIGH TERRAIN.

[christchurchguy]

lately it looks like there is a bit of inflow in the low clouds to the south to the low into the convection

[Caribwxgirl]

It's starting to really look interesting on satellite IMO