cieldumort
(Moderator)
Thu Aug 03 2017 02:16 AM
HUR. GERT Lounge



A vigorous and fairly sizable wave rolling off the westernmost tip of Africa this morning has the interest of many models. Conditions for development this week and into next are much better than encountered by recent waves which attempted to get going within the monsoon trof in the central-east Tropical Atlantic (see Lounge).

As of the August 3, 2017 2AM TWO, NHC has assigned 50-50 odds that this wave becomes a tropical cyclone within 5 days. It is worth noting that forecast environmental conditions suggest that this feature could become a long-track hurricane. Movement is likely to be west or west-northwest at 10 to 15 mph for the next several days.

Invest 99L has become TD8 and the title has been updated. - Ciel


MikeCAdministrator
(Admin)
Thu Aug 03 2017 07:41 AM
Re: Significant E Atl Wave (99L)

Long range speculation includes watching the global (and other) forecast models to watch for trends, when a system is still an invest and not fully developed things can (and do) change wildly from run to run, but they tend to vary less as time goes on. These models are helpful in that they give a general path to look for, and we look for consensus and stability between runs to gauge confidence in what they do. many times the position of the system in the model isn't as important as the conditions (Ridges/troughs/lows/upper level lows/dry conditions) around it.

That said, here's the first model set for 99L:

0z Euro: Not as strong as it was on the prior run, but it has it crossing the leewards as a Tropical Storm Tuesday night, then falling apart int the Caribbean afterwars (another system near the Yucatan starts going in the Bay of Campeche).

6z GFS: Develops a hurricane around 40W in the Central Atlantic Monday morning, keeps it north of the Caribbean islands, and bends it back west (north of the Bahamas), and has a major hurricane landfalling in coastal Georgia near Brunswick/St..Simons on Thursday August 17th (2 weeks from today). The 0z run prior to this had the same result. After landfall the 6z GFS turns it northward inland over North Georgia then eastern Tennessee (Knoxville) into Kentucky and Indiana weakening rapidly. (with a ton of rain).

The fact the models want to push this so far west implies the high will be strong around that time, which would increase the odds for some sort of impact on the land US down the road, if it doesn't stay south and go through the Caribbean like the current Euro Shows. So some sort of impact is likely, to what degree and where (islands vs US) is still up in the air. If the trend moves east during the next few runs, out to sea becomes more likely.

Way too early to say which is going to be more correct, nothing has developed yet, and the first runs are typically very wrong.



MikeCAdministrator
(Admin)
Thu Aug 03 2017 01:19 PM
Re: Significant E Atl Wave (99L)

12Z GFS run seems a bit off on initialziation (phantom wave from the real wave?) But is east and out to sea this time, with no direct landfall.

M.A.
(Weather Hobbyist)
Thu Aug 03 2017 04:01 PM
Re: Significant E Atl Wave (99L)

So far it looks to be a fish spinner. Bermuda could see some of this one. The CV season is upon us.

MikeCAdministrator
(Admin)
Thu Aug 03 2017 05:25 PM
Re: Significant E Atl Wave (99L)

12z Euro is still into the Caribbean, so I wouldn't jump to that conclusion this far out, I pointed out the GFS had a bad init latching onto a phantom area rather than the actual low, (too far west), I think the answer is somewhere in the middle.

MikeCAdministrator
(Admin)
Thu Aug 03 2017 07:47 PM
Re: Significant E Atl Wave (99L)

18Z Gfs is back further west with a much closer approach to the Bahamas on August 13th, but not over, and then makes landfall as a major hurricane on the NC outer Banks near Morehead City on August 15, heads over Hampton Roads/Norfolk and back out into the Atlantic then races over eastern Long Island and over Boston on august 16th. Slightly better init than the earlier run. GFS does not really develop invest 90L (the other one being tracked) in the bay of Campeche at all.


Esemble spread is biased toward the east.

Still a lot of uncertainty there, but 99L will likely be a long lived tropical system that can be watched over the next week or two. The leewards still need to watch it also, the GFS seems to be overdoing development right now.





MikeCAdministrator
(Admin)
Fri Aug 04 2017 12:08 AM
Re: Invest 99L Lounge

0z gfs run rolling in so far it looks like it will miss the Caribbean to the north on this run, however Euro will still likely take it into the Caribbean. Closest approach for the Caribbean is Thursday night into Friday. At this far into the run (+186 hour) it's slightly south of the prior 18z run. Ridging to the north is fairly strong also.

After this, it gets very close to the Turks and Caicos islands in the Bahamas, enough to be a problem there. Into the central Bahamas late August 12th into the 13th. Bermuda high is strong, major hurricane over Nassau on the 13th.

Late evening on the 13th, its very close to Florida, very close or just over Cape Canaveral (925mb major hurricane) but stays just offshore (very similar to Matthew), eventually landfalls near Savannah/Hilton Head on Aug 15th, a bit weaker, then rides inland through North Carolina.

earlier runs of the CMC misses the islands and takes it out to sea, the UKMET rides it through the northern Caribbean islands (weak)

The newer 0z run of the CMC is weaker, but much further west.

Splitting the difference takes it very close to the northern Caribbean islands, maybe skimming Hispaniola after missing Puerto Rico barely to the north.

HMON/HWRF develop it into a hurricane in about 5 days.

In short still too soon to tell impacts, about a 50/50 split for Caribbean impact, and much less for US/Bahamas impact, but more than earlier. A slight shift to the west. The most alarming thing about the GFS is the 600dm ridge that holds for several days, which would likely force the storm west and raises the chances of land impacts a great deal (taken in isolation, if the trend holds, even more so)

99L needs to be watched VERY closely over the next week and a half.




MikeCAdministrator
(Admin)
Fri Aug 04 2017 06:15 AM
Re: Invest 99L Lounge

To balance out the 0z gfs run, the 0z Euro run weakens it a bit before crossing over the Leeward islands on Wednesday then rapidly weakens it in the eastern Caribbean and it gets torn up near Hispaniola and brings some rain to Jamaica as a weak low, Friday August 11th. Interesting to note that the The Euro is faster with the system forward movement than the GFS.

The GFS shifted back a bit east, missing the Bahamas and Florida this time, gets very close to Cape Hatteras on Aug 15th and close to Cape Cod on the 16th, but it stays east and recurves it out.

The Euro halso has a strong rdige, but it keeps the system in the Caribbean. So the 50/50 shot for going north or through the islands is still there.

System is important to watch, but way too early to say where it winds up.


M.A.
(Weather Hobbyist)
Fri Aug 04 2017 07:19 AM
Re: Invest 99L Lounge

This is certainly grabbing my attention. Looks to be a very interesting week to come. Still hoping for a fish spinner.

MikeCAdministrator
(Admin)
Fri Aug 04 2017 09:02 AM
Re: Invest 99L Lounge

the GFS seems to be really overdoing intensity on 99L, so I suspect it's a bit off. It may be a close call for the Leeward Islands. Particularly since dry air will stall any development today or tomorrow.

On the normal model plots, I'd think the TVCN is most likely (This doesn't mean much, however)


MikeCAdministrator
(Admin)
Fri Aug 04 2017 11:34 AM
Re: Invest 99L Lounge

!2Z GFS starting to roll in, starts off weaker than the last run, but recovers at 24 hours. (Yesterday's 12Z run already had it as a Tropical storm right now, and obviously that didn't happen)

By 48 hours, the position is about the same as the 6z run, but its a bit weaker. TD/tS vs hurricane.

by 96 hours it moves faster and a bit further south of the earlier run, this appears to be closer to the Euro run, although it is a strong Tropical Storm at this point. This run seems more realistic toward actual conditions than the prior run.

At 120 hours out it is much further southwest than the earlier run, and nearing the northern leeward islands, tropical storm strength.

Near/over St. Johns and Barbuda in the Leewards on Thursday morning as a Tropical Storm then moves over/near St. Kitts, toward the Virgin Islands.

Tropical Storm landfall on Puerto Rico Thursday night, then moves toward Hispaniola, by friday night it's over Haiti and getting torn apart. By Saturday morning the remains are over Guantanamo in Cuba.

By Monday, August 14th it emerges west of Cuba into the Gulf and gets a little stronger, maybe a TS again, then heads toward southeastern Louisiana with a TS landfall late afternoon on the 15th.


This is closer to the Euro run and much weaker (never gains hurricane strength) and stays weak.


MikeCAdministrator
(Admin)
Fri Aug 04 2017 02:42 PM
Re: Invest 99L Lounge

12Z Euro does not develop 99L, moves it into the Caribbean.

MikeCAdministrator
(Admin)
Fri Aug 04 2017 09:01 PM
Re: Invest 99L Lounge

18Z GFS back to something.

Strenghtens to a TS around Monday/Tuesday in the Atlanta, weakens a bit as it gets closer to the Leewards, goes over Barbuda Late Wednesday night into Thursday morning, barely misses Puerto Rico to the north on Friday, then stays just north of Hispaniola, Stays north of Cuba, Goes over the middle Florida Keys on Sunday August 13th as a major hurricane, ,rides just offshore of the west coast of Florida as a major hurricane. Landfall near Panama City, FL on August 14th, as a major hurricane, then up through Alabama/Georgia and Eastern Tennessee,


MikeCAdministrator
(Admin)
Sat Aug 05 2017 08:26 AM
Re: Invest 99L Lounge

Overnight model runs show a much weaker system, GFS an Euro included, the Euro does not develop 99L at all, while the GFS does develop a tropical storm that crosses the leewards Wednesday Morning then weakens and eventually dissipates over Hispaniola. The NHC is slowly dropping chances for development based on the Euro's persistence in not developing the system.

The storm's forward motion has been faster than earlier GFS model runs showed.


MikeCAdministrator
(Admin)
Sat Aug 05 2017 12:02 PM
Re: Invest 99L Lounge

12z operational GFS run continue to keep the system weak, and moves it into the northern Leeward islands a depression or wave Wednesday night into Thursday. Weakens it into a wave and clips the eastern side of Puerto Rico on Thursday. The main vortex stays north of Hispaniola on this run, but it remains weak (just a wave/TD) on Friday then loses it entirely.




MikeCAdministrator
(Admin)
Sat Aug 05 2017 02:21 PM
Re: Invest 99L Lounge

12Z Euro is a bit stronger for this system than prior runs, shows potential for development for 99L Tue-Wed where before it did not. This is very similar to the 12z GFS run this time, with the system north of Puerto Rico on Friday, but as a wave or weak depression. Just a bit slower.


The elongated nature of this system is making it difficult for anything to get going, but general conditions aren't bad for it, it has two competing areas for a center to develop, and neither is winning out right now.


MikeCAdministrator
(Admin)
Sun Aug 06 2017 08:10 AM
Re: Invest 99L Lounge

This mornings runs have brought concern back to 99L.

The 0z Euro now moves the system north of the Caribbean, and starts to develop it a week from today (aug 13th) east of the Bahamas, at the end of the run (Aug 16) there is a hurricane sitting off south Carolina, with it still moving toward land.

The 6Z GFS is similar but it clips the northern Bahamas on August 13th, as a weaker system, then bends it back north for a near landfall between Charleston and Myrtle Beach on Aug 15th and then rides along the coastline through the outer banks.

Still too far to say much of anything about this system other than continue to watch it.


IsoFlame
(Weather Hobbyist)
Mon Aug 07 2017 10:23 AM
Re: Invest 99L Lounge

With the 25th anniversary of Hurricane Andrew approaching, initially weak, long-track 99L will be monitored for any potential to rapidly develop ITVO the Bahamas late weekend/early next week- especially if the ridge strengthens to the north of the system about the same time.

JMII
(Storm Tracker)
Mon Aug 07 2017 11:00 AM
Re: Invest 99L Lounge

Any Cape Verde storm that pops up normally catches and keeps my attention. With so much warm water to traverse the potential for a strong system is higher then normal. The models have clustered a bit further north and currently 99L's development is less favorable so hopefully those trends continue.

MikeCAdministrator
(Admin)
Mon Aug 07 2017 11:14 AM
Re: Invest 99L Lounge

Not much to update with 99L, none of the major models do anything with it anymore, but it still is a good idea to Monitor, particularly when it gets north of the Caribbean.

MikeCAdministrator
(Admin)
Mon Aug 07 2017 02:33 PM
Re: Invest 99L Lounge

Euro is back to showing development of 99L, this time north of the Caribbean as a Tropical Storm in about 76 hours, and it moves generally west, keeps north of the Bahamas at 144 hours out and slowly starts to curve north by 168 hours out. No landfall, but cuts it close to the Outer Banks,.

The 12z GFS does not develop it.


MikeCAdministrator
(Admin)
Tue Aug 08 2017 10:44 AM
Re: Invest 99L Lounge

Euro shows a developing storm off the east coast next week (Development starts around Saturday), but does not make landfall and recurves it out to sea.

6Z GFS does not develop 99L at all.


MikeCAdministrator
(Admin)
Wed Aug 09 2017 06:18 AM
Re: Invest 99L Lounge

This morning is no different than the last run, with the consistancy it is very likely that the system will stay out to sea, we'll keep monitoring it in case thus changes, but as of now there isn't much reason to go against the idea of a recurve which is good news for the east coast.

MikeCAdministrator
(Admin)
Wed Aug 09 2017 02:47 PM
Re: Invest 99L Lounge

12Z euro showing development still, but recurving it similar to earlier runs. The system has a fairly decent center, but no persistent circulation. Chances have gone back up to 50% for 5 day development.

GFS, however, still does not develop it.


MikeCAdministrator
(Admin)
Thu Aug 10 2017 05:26 AM
Re: Invest 99L Lounge

This morning the Euro ahs stopped developing this system, the energy with it remains offshore, however. The GFS also shows no development.

cieldumort
(Moderator)
Thu Aug 10 2017 12:16 PM
Re: Invest 99L Lounge

When the sun set on 99L last night, Wednesday Aug 9, a tight low level circulation was evident, and for several hours deep convection fired in association with it. But as the night (and shear) wore on, most convection became displaced from the incipient low level center, and by the time an ASCAT pass made it over, the fledgling disturbance had degenerated back into a sharp wave.

Model support has fallen apart on 99L within the past day, but it has been and remains a tenacious wave. Just this morning it already appears to be trying to consolidate a low level circulation again, with a little convection attempting to hold.

As models have mostly shut off the entire basin for the next ten days to two weeks, which given the higher sea level pressures is somewhat understandable but may very well be overdone, this could be producing a bias to miss the smaller and less pronounced features that only need 'a break' to develop. 99L would certainly qualify.

Should 99L not develop, or develop late, it might pose more of a threat to the US later on, as it would be less likely to recurve sooner.


JoshuaK
(Weather Guru)
Fri Aug 11 2017 01:09 PM
Re: Invest 99L Lounge

I'm seeing two distinct circulation areas for 99L at the 15:45 UTC timeframe. The first appears to be an LLC centered at about 22.2N and 65.8W or on the western edge of the convection. The second looks to be a mid-upper level COC and appears to be centered at roughly 22.2N and 63.2W.

cieldumort
(Moderator)
Sun Aug 13 2017 06:13 PM
Re: TD EIGHT Lounge

TD8 has become Gert, the seventh named storm of the 2017 Atlantic Hurricane Season. The Lounge title will be updated accordingly. Officially forecast to max out as a 65 MPH storm at each of the following plots, it is possible that Gert also attains hurricane status, even if only for a while between them.
Quote:


FORECAST POSITIONS AND MAX WINDS

INIT 13/2100Z 28.1N 71.7W 35 KT 40 MPH
12H 14/0600Z 29.3N 72.1W 40 KT 45 MPH
24H 14/1800Z 31.1N 72.1W 50 KT 60 MPH
36H 15/0600Z 32.9N 71.3W 55 KT 65 MPH
48H 15/1800Z 35.1N 68.8W 55 KT 65 MPH
72H 16/1800Z 39.8N 59.1W 50 KT 60 MPH
96H 17/1800Z 45.0N 44.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 18/1800Z...DISSIPATED




cieldumort
(Moderator)
Wed Aug 16 2017 10:56 AM
Re: HUR. GERT Lounge

Gert is attempting to be declared the first Major Hur of the 2017 Atlantic Hurricane Season. Even though the most recent advisory has Gert as a 90MPH hurricane, the cyclone appears to be in a powerful intensification phase, possibly rapid, and the 90MPH advisory estimate is almost certainly much too low.

Most recent satellite derived Current Intensity estimates as follows:
Quote:


CURRENT ESTIMATE
Date (mmddhhmm): 08161158
SATCON: MSLP = 964 hPa MSW = 98 knots
SATCON Member Consensus: 93.0 knots
Pressure -> Wind Using SATCON MSLP: 105 knots
Distance to Outer Closed Isobar Used is 160 nm
Eye Size Correction Used is 5.4 knots Source: MW

Recent Member Estimates

ADT: 965 hPa 85 knots Scene: CDO Date: AUG161115
CIMSS AMSU: 965 hPa 89 knots Bias Corr: 0 (MW) Date: 08161052
SSMIS: 962 hPa 96 knots Date: 08161158





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