cieldumort
(Moderator)
Sun Sep 02 2018 02:19 PM
Isaac Lounge



Yet another African Easterly Wave is about to roll off that continent and into the far eastern Atlantic. This feature has just been given an opening bid of 20% development odds within 5 days by NHC, and may be Invest tagged within a day or so (will update title as needed).

NHC:
Quote:

A tropical wave located along the west coast of Africa is forecast to move westward over the far eastern tropical Atlantic for the next several days. Upper-level winds are expected to gradually become more conducive for some slow development of this disturbance by the middle of the week.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...low...20 percent.



As noted by NHC in the TWO quote above, conditions for near-term development are not good, and do not look nearly as good overall within a five day window as they did for pre-Florence. That said, a weaker wave is likely to track more west - which could mean more of a concern for the Caribbean or central America to the U.S. possibly as soon as 7-10 days out.

Title edited. This is now Invest 92L. 92L is now TD9. NINE will likely be named within 24 hours. The next names on the list are Helene and Isaac. TD9 was named Isaac with the 9/8 5PM Advisory - Ciel


MikeCAdministrator
(Admin)
Mon Sep 03 2018 09:47 AM
Re: New: E ATL Wave

Advance model runs suggest this one is worth watching closely, also, currently 30% chance for development.

Euro has it approaching the lesser Antilles 10 days out,

6Z GFS Crosses the lesser Antilles then gets shread apart over Hispaniola.

6Z FV3 GFS has it further north, crosses the Bahamas, and then landfalls near Ft. Lauderdale September 18th as a category 3 hurricane.

Canadian does nothing with it at all.


cieldumort
(Moderator)
Wed Sep 05 2018 05:28 AM
Re: 92L Lounge




The 0458z 85GHz Composite image above that "sees through" Invest 92L suggests that the disturbance may now or will very easily soon be a Tropical Depression. Also, based on the curvature of convection and the location apparent greatest convergence, may be centered a little north of prior tracking (if so, likely impacting future track). TBD.

90% Development now per NHC. The next name on the list in the Atlantic is Helene.


cieldumort
(Moderator)
Wed Sep 05 2018 11:34 AM
Re: 92L Lounge

There was indeed an overnight jump in where the disturbance is centered. From 11N 26.6W at 05 06z to 12.4N 27.4W at 05 1200z.. It is not clear to me if 92L was analyzed much too far south to begin with, or if a new center began to take over, but it looks to be the former.

This will have impacts on model runs going forward, possibly not only changing models' forecast track and intensity of this Invest, but potentially even tweaking some of the steering currents and environments around Major Hurricane Florence, as well as that of waves behind it.

Visible imagery better shows that 92L is not yet nearly a tropical cyclone as the Composite microwave image in the entry above suggested as possible. While a healthy structure exists, the disturbance does not yet have enough organized deep convection.

NHC 50% within 48 hours, 90% within 5 days


MissBecky
(Weather Guru)
Thu Sep 06 2018 05:36 AM
Re: 92L Lounge

Looks like 92L is on a few radars, so to speak. From the Tampa Bay NWS office, in their forecast discussion:

As we enter the longer range timeframe into the middle of
next week, all eyes will be on Hurricane Florence as it
continues to meander west to northwest over the open
Atlantic. There remains very little if any agreement amongst
the longer range models regarding the potential track of
Florence, but all interests along the Atlantic Coast from
the Carolinas northward should pay very close attention as
we move through time. At this time it appears Florence
should remain well north and east of the Florida peninsula,
but other tropical waves continue to move off Africa with
decent odds of development. These could eventually become a
concern beyond the 7 to 10 day timeframe, and we will be
monitoring their progress closely. We are nearing the peak
of Hurricane Season so it is no surprise to see an uptick in
activity. Now is a good time to make sure you hurricane
safety plan in in order. If you do not yet have a plan, its
time to get one.


MikeCAdministrator
(Admin)
Thu Sep 06 2018 07:08 AM
Re: 92L Lounge

Quick model summary, a lot depends on what happens to Florence for 92L

6z GFS, by next friday (!4th) just north of the lesser antilles, rides north of Puerto Rico, over the northern part of HIspanoila, by Sep 16, over most of Cuba, in Gulf by Sep 18th, starts to strengthen, Cat 2 landfall in Tampa Bay the afternoon of Wednesday, Sep 19th. Back in the Atlantic by midnight on the 20th out by St. Augustine, over the outer banks on the morning of the 21st, the rides along the shore toward NJ.

0z Euro, blocked by Florence recurves east of the lesser Antilles. GFS FV3 also does this.

0zCMC Launches it straight north this friday into the open Atlantic.

0z UK generally follows GFS track up until the UK run ends.


OrlandoDan
(Weather Master)
Sun Sep 09 2018 06:54 AM
Re: 92L Lounge

Was checking out the GFS for Isaac and current run takes him well south of the US. What do the experts here think?

MikeCAdministrator
(Admin)
Sun Sep 09 2018 08:44 AM
Re: 92L Lounge

Current indicators is that it'll be a Caribbean runner, and probably weak when it does. Conditions get really hostile for it.in the east Caribbean.

MikeCAdministrator
(Admin)
Sun Sep 09 2018 08:22 PM
Re: 92L Lounge

Isaac Models

12Z Euro: Landfall near Guadalope as a cat 3 Thursday morning then goes "poof" in the Central Caribbean
18Z GFS Tropical Storm near Guadalope Thursday morning, then poof.
18Z FV3 GFS Tropical Storm north of Guadalope Thursday midday, then poof
18Z Icon Tropical Storm north of Guadalope Thursday night then poof
12Z CMC turns out to sea just before reaching the NE Caribbean
18Z HWRF Ends the run with a cat 5 east of Barbuda


JMII
(Weather Master)
Mon Sep 10 2018 01:47 PM
Re: 92L Lounge

I'm flying to Puerto Rico today to do some work related stuff down there. They have already told us to get out before Friday, so I've got a Thursday AM flight back booked. Storm looks to stay south of the island and weaken once its that far west, but we are not taking any chances. The outflow from Helene is currently limiting Issac a bit but that should lessen as Helene turns north. Today is technically the historical peak of hurricane season... and it sure looks that way on the satellite image.

B.C.Francis
(Storm Tracker)
Mon Sep 10 2018 05:15 PM
Isaac

Not to get away from Florence, but does Isaac have a chance to make it through the graveyard and what is going to stop him from making a curve west north west or northwest.

danielwAdministrator
(Moderator)
Mon Sep 10 2018 05:49 PM
Re: Isaac

Just checking in. But at Isaacs low latitude I would give It a 50/ 50 on making it into the Eastern Caribbean intact.
There have been.a few storms over the past several years that did make it into the Eastern Caribbean by skirting the Islands or threading the needle.


cieldumort
(Moderator)
Mon Sep 10 2018 09:34 PM
Re: Isaac

Being a smaller TC, Isaac is subject to large fluctuations up and down, and whether or not he survives a trip through the 'graveyard' (let alone make it there - which is the official forecast, and most possible but far from certain scenario), may come down to the exact timing of any such ups and downs.

I haven't been focused much on Isaac, myself. Three systems much closer and with far greater likelihood of impacts, but will review 0z models by morning.


JMII
(Weather Master)
Mon Sep 10 2018 09:47 PM
Re: Isaac

Issac got really torn up today and the shear is expected to increase, not sure he can survive given his small size. If he continues to stay weak he'll track due west however if he can maintain himself (which the NHC believes) he might start to drift along the northern edge of the current cone putting PR into the picture. Almost all model guidance keeps him south of PR and in a weak state. The ridge that is pushing Florence west is also keeping Issac down south. This same ridge has basically created a wall that is sending Helene due north. Incredible to see 3 storms all bouncing off the same feature and moving away from each other like billiard balls.

cieldumort
(Moderator)
Tue Sep 11 2018 04:06 AM
Re: Isaac

Quote:

Not to get away from Florence, but does Isaac have a chance to make it through the graveyard and what is going to stop him from making a curve west north west or northwest.




This is a really important question for us to be considering here in the Lounge and thank you for bringing it up, B.C.

So Isaac has been a bugger for NHC all along - the least reliable model guidance. Huge spreads. Vastly different among many members and runs with regard to intensities, and tracks.

But it looks like the not-very-favorable, but just-favorable-enough environment will continue, with the chance of either becoming a Major within the next 3 or 4 days, or devolving into a wave, decreasing. This suggests that a continued track generally west for the next 3 to 4 days as either a Trop Storm or Cat 1 Hur looks reasonable, and a composite of the 0z model runs seems to bear that out as a general consensus.

After days 3, 4 or 5 is where things get ... different. Big spreads again. However, I would posit that there is a model averaged implied just over 60% chance that Isaac retains coherence as a Tropical Cyclone beyond his trip up to or into the graveyard (I say 'up to,' because there looks to be a slight, but non-negligible chance Isaac hooks right (north) prior to entering the Caribbean). And maybe even a 75% chance of continuing on past Day 5, if allowing for a period of having fallen apart, but only to come back together again at some point within a roughly 4 to 8 day window from now.

In summary, if these best educated guesses are about right, Isaac (or his remnant) may be much more one to watch than not beyond just his trip to the Antilles.


JMII
(Weather Master)
Tue Sep 11 2018 10:27 PM
Re: Isaac

Isaac is just so tiny, amazed its still together in this hostile environment and the NHC predicts it continues to hang in there as TS on its westward track. PR appears to be safe now with the storm staying way south and being too weak to bring anything more that typical daily rain and a light breeze to the island.

I can say driving around PR today nobody seems worried at all. However damage from Maria is still visible here, many trees are stripped of leaves and some traffic lights are out. The locals claim that they operate on "island power" and are used to rolling mini-black outs that effect small areas in tiny spurts. I will say cell coverage has been no problem with AT&T for me but Verizon is more spotty. This is second time I've been on the island and being from Florida I completely forgot just how many mountains are here, its very odd seeing palm trees on such steep terrain. The hills remind you of just how bad the flash flooding must be in a tropical events here in this part of the world. Its one thing to have rain, but its completely different deal when something (like Florence or Harvey) dumps several inches that all roars downhill doing way more damage versus the slow pooling or over flowing pond style flooding we get in FL or TX where the terrain is so flat.


JMII
(Weather Master)
Wed Sep 12 2018 08:22 PM
Re: Isaac

Isaacs center is completely exposed, so its basically done. However the NHC continues to believe it will maintain TS status during what looks to me as an almost impossibly long run due west over the weekend.

OrlandoDan
(Weather Master)
Thu Sep 13 2018 06:04 AM
Re: Isaac

I see Isaac is expected to make a turn to the Northwest at the end of the current forecast period. What do the experts think of the atmospheric conditions that will allow him to strengthen in the gulf and what are thoughts on longer term track? Florida?

IsoFlame
(Weather Guru)
Fri Sep 14 2018 06:13 PM
Re: Isaac

Tropical Storm Isaac Discussion Number 29
NWS National Hurricane Center Miami FL AL092018
500 PM AST Fri Sep 14 2018

It has been a very interesting flight of the NOAA Hurricane Hunter aircraft this afternoon. Dropsonde and SFMR data indicate that the maximum winds are around 35 kt again, and the pressure has fallen to about 1002 mb. However, the system is tilted southward with vertical height due to northerly shear, and scatterometer and Hurricane Hunter tail-Doppler radar data indicate the system is elongated from northeast to southwest, albeit closed. Note that the plane was unable to sample the southwestern quadrant well because of strong convection and intense lightning, so the flight-level winds showing no circulation were unrepresentative.

The intensity forecast hasn't gotten any easier with Isaac.Vertical shear is expected to decrease a bit more, which might
diminish the effects of dry air seen on water vapor images around the cyclone. However, the GFS and ECMWF continue to insist that Isaac will degenerate into a wave within the next 2 or 3 days, which is almost unanimously supported by their respective ensemble members. This is the solution that the official forecast follows. It should be noted that none of the global models show pressures this low now with Isaac, except the UKMET, and that model is the one that holds onto the circulation the longest. The reality of the situation is that the long-term future of Isaac is cloudy, and the best advice is just to follow NHC advisories every 6 hours to see if we gain any confidence.

Isaac is moving westward at about 12 kt. A ridge over the southwestern Atlantic should steer the cyclone westward over the weekend then west-northwestward early next week as Isaac reaches a weaker portion of the ridge. Just like yesterday, a stronger system would likely turn more to the west-northwest earlier, moving closer to Jamaica. Since the system is forecast to be weaker, the forecast lies on the westward and faster side of the guidance, and should also be considered low confidence since it depends on the intensity. Interests in Jamaica should monitor the progress of the
Isaac.

FORECAST POSITIONS AND MAX WINDS

INIT 14/2100Z 15.3N 68.2W 35 KT 40 MPH
12H 15/0600Z 15.4N 70.1W 35 KT 40 MPH
24H 15/1800Z 15.4N 72.2W 35 KT 40 MPH
36H 16/0600Z 15.7N 74.2W 35 KT 40 MPH
48H 16/1800Z 16.2N 76.3W 30 KT 35 MPH
72H 17/1800Z 17.5N 80.0W 25 KT 30 MPH
96H 18/1800Z...DISSIPATED


cieldumort
(Moderator)
Sat Sep 15 2018 06:38 PM
Invest Isaac

Isaac devolved into a stout wave last night, with maximum sustained winds of roughly 35 MPH and minimum pressure of 1006 MB. Convection continues to flare intermittently while the wave tracks through the central Caribbean, with occasional, but transient consolidation of both winds and convection about embedded mesolows.

Conditions for development throughout the entire tropical Atlantic appear to be entering a much less favorable phase that may last a week or even two, but it does still appear that the remnant of Isaac may benefit from a region of slightly more conducive conditions in the western/northwestern Caribbean - into possibly also the western Gulf - next week, provided the disturbance lasts long enough to avail itself of this.

Interests in the northwest Caribbean, Yucatan and western Gulf of Mexico may want to monitor this feature closely.


cieldumort
(Moderator)
Sun Sep 16 2018 05:43 PM
Re: Isaac Lounge

For all practical intents and purposes, Isaac appears to behave like an off-and-on TD since its Final Advisory was written.

More recently, the old, primary LLC has become prominent again, with scatterometer passes showing a well defined surface circulation, but with visible satellite confirming only somewhat organized deep convection. However, trends this afternoon suggest that with the LLC now exiting the region of higher shear that exists over the central to eastern Caribbean, convection may be getting better organized, and it is looking more possible that Isaac may end up a TD or even a tropical storm again.

Movement the past two days has been towards the west-northwest to northwest. Interests in Hispaniola, Jamaica, Cuba, Yucatan peninsula and the Lower Keys may want to monitor this system closely. Heavy rains and gusts to tropical storm force are already occurring regardless of classification.


cieldumort
(Moderator)
Sun Sep 16 2018 06:41 PM
Re: Isaac Lounge

Timely images

(Top): SSMIS F-18 Composite microwave from 2211z today lines up well with the blowup of banding convection and lighting that looks to be collocated with Isaac's re-energized LLC (Bottom).

Isaac may be very close to if not now becoming a bona fide TD again while just east of Jamaica.




cieldumort
(Moderator)
Mon Sep 17 2018 02:45 AM
Re: Isaac Lounge

09/17 0z models are rolling in. So far, one concerning. The rest, not so much.

HWRF - TD by 09z Tuesday. Tracks through Straits of Yucatán, clipping extreme western Cuba, as a 999mb Tropical Storm early Wednesday. Enters southern Gulf Wednesday afternoon and begins deepening at a healthy clip. 979mb Cat 2 hurricane by 06z Friday in the central Gulf. 975mb Cat 3 Major by 18z Friday south of Louisiana.

HMON - Basically analyzes Invest Isaac as a TD already, and thus initializes the run as such. Devolves into a wave that appears to track into the Gulf though end of run.

GFS - 0z begins as a sloppy open wave. Eventually crosses into Mexico by 0z Sat without developing.

FV3 GFS - 0z begins as a sloppy mostly open wave. Washes out in the Bay of Campeche by 06z Friday.

ICON - 0z begins with mostly closed 1008mb Low centered just east of Jamaica. Opens/closes/opens/closes and stays weak across Straits of Yucatán, finally stalling out and closing back off near Corpus Christi, TX by 09z Sunday. Washes out over deep south Tx as a likely heavy rain maker.

CMC - 0z begins as a sloppy open wave, after having analyzed it as closed off during the day Sunday. Closes back off by 18z Monday with a 1010mb Low. Opens and closes again. Closed weak Low in southern Gulf by 18z Wednesday. Remains mostly wavy with vort max tracking into SE TX by 18z Friday.

ECMWF - 0z begins as a weak closed Low centered just southeast of Jamaica. Opens back up and splits in two by 0z Thursday. By 0z Friday the southern extent of trof crosses Yucatan and into BoC, with the northern branch tracking across Keys. Breezy showers likely for each location, but no tropical cyclone.

ECMWF Ensemble-implied probability of TCG within 72 hours (from 09/16/12z run): 25%

As a side note, after looking good throughout the day Sunday and into early night, Invest Isaac looks to be getting hit with some northerly shear, having not tracked west enough yesterday to avoid it, and is on a dramatic weakening trend at this time.


cieldumort
(Moderator)
Mon Sep 17 2018 12:30 PM
Re: Isaac Lounge

Conditions for Isaac's development in the SW ATL at the start of this new week are less favorable than what was being advertised a week ago. Additionally, the now former tropical cyclone is in even worse shape than what most models were expecting just a few days ago. Really, the only model left that redevelops Isaac is the HWRF, but this is not a reliable genesis model, and has been too bullish on Isaac all along. NHC has unsurprisingly lowered the odds of TC formation down to just 10%. ECMWF ensemble implied probably of formation is even less.


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