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TD-like #94L has moved inland over Central America with heavy rains and gusty winds. Wave approaching Antilles but shear is high.
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General Discussion >> 2018 Forecast Lounge

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cieldumortModerator
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C Am. Gyre (91L, 97E, 94L etc)
      #99686 - Sun Sep 30 2018 06:53 AM

For several weeks now many models have been hinting at TC formation in the southern Caribbean during the first week of October - possibly as an offshoot of a Central American Gyre (CAG). While development of a robust CAG is looking less likely, and the time frame for tropical cyclogenesis has been getting pushed out, models in total now seem to be honing in on the October 4-8 range for a TD to form in the Caribbean.

At this time it looks like the most likely source for formation will come from a mix of a new tropical wave, the remnants of Kirk, and perhaps a weak CAG. It does not look likely that such a system would retain the name Kirk, but possibly, in which case this thread would get merged with the existing Kirk Lounge.

Early October is very much a climatologically favored part of the season for TCs in this region to develop and track north to northeastward, and rarely northwestward. At this time the model breakdown from 09-30-0Z is as follows:

ECMWF - Genesis by 0z Oct 8 heading north. Sloppy TD or Inverted Trof through end of run 0z Oct 10.

GFS - Genesis by 18Z Sat Oct 6. Brief DR & Bahamas impact as a sloppy TD or weak storm, then out to sea

GFS FV3 - Genesis by 0z Oct 7. Cat 2 hurricane landfall on SC/NC border by 12Z Oct 10

CMC - Genesis by 12Z Sun Oct 7. Blocked by building High to the north and tracks NW. Cat 1 in southern Gulf by end of run on 0z Oct 10

NAVGEM - Genesis by 0z Oct 6. Blocked by building High to the north and tracks NNW. Nearing western Cuba as a strong Trop Storm at end of run at 12Z Sun Oct 7.

ICON - Genesis by 0z Oct 4. Very little movement in central Caribbean through end of run at 06Z Oct 6 as a 994 MB trop storm by that point.

This feature has not yet formed and does not yet have an Invest tag, but the precursor systems appear to be coming in place for a good chance of tropical cyclogenesis next week, and the title will be updated or merged as appropriate.

Title changed to Central American Gyre. It now looks like a CAG is indeed forming over the western Caribbean and will likely stay locked in place for a while because of a blocking pattern. Given these forecast steering currents, multiple spin-off systems (of unknown intensity still) may form, in addition to the heavy, flooding rains occurring within the parent Gyre itself. - Ciel

Edited by cieldumort (Sun Oct 14 2018 05:03 PM)


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MikeCAdministrator
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Re: Possible Caribbean Dev Early Oct [Re: cieldumort]
      #99688 - Sun Sep 30 2018 07:09 PM

The 18Z GFS shows a hurricane landfall from this area on Thursday October 11th near Ormond Beach. Extremely unlikely. (East coast hits are very unusual in October). Considering the 12Z run showed this area shooting off to the northeast well away from land it's very difficult to take seriously.

The CMC develops this more in the West Caribbean, and the Euro shows it as a weak area over the Bahamas on the 10th. All that is good for is that next weekend into the second week of October should be the time to watch this system.


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IsoFlame
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Re: Possible Caribbean Dev Early Oct [Re: MikeC]
      #99689 - Sun Sep 30 2018 10:46 PM

It would be very unusual for the 18Z GFS system to retrograde onto the Florida peninsula from the Atlantic, then take nearly 2 days to crawl across north-central FL. Given Florence and Leslie's behavior "going against the grain" at higher latitudes by tracking W/SW then meandering nearly in place before ejecting NE (forecasted for Leslie), the October storm ("Michael"?) might just extend of the trend.

Edited by IsoFlame (Sun Sep 30 2018 10:51 PM)


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cieldumortModerator
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Re: Possible Caribbean Dev Early Oct [Re: cieldumort]
      #99690 - Sun Sep 30 2018 11:57 PM

12z Sunday GFS 500 hPa anomaly forecast for 12Z Monday Oct 8 shows why anything that forms during the next several days too far west (perhaps anything developing west of 70W) and south of 30N is likely to be forced back towards the west (U.S., Mexico and/or central America). Highly anomalous and subject to change, but globals are collectively starting to buy in to this.



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cieldumortModerator
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Re: Possible Caribbean Dev Early Oct [Re: cieldumort]
      #99691 - Mon Oct 01 2018 05:19 PM


Image cr: Weathernerds.org

Disturbed weather in the central Caribbean today is related to a nearly stationary surface trof (part of old x-Kirk), interacting with an upper-level trof to its northwest, and the initial stages of what could become a large Central American Gyre, presently centered near Costa Rica.

Tropical Cyclone development by week's end looks very possible, although still no outline in the 5-Day TWO from NHC.


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IsoFlame
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Re: Possible Caribbean Dev Early Oct [Re: cieldumort]
      #99693 - Tue Oct 02 2018 10:05 AM



Strong convection firing this morning east of the surface trough. I'd place money on the current 20% 5-day development chance jumping up with the next outlook update.

Edited by cieldumort (Tue Oct 02 2018 01:29 PM)


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cieldumortModerator
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Re: Possible Caribbean Dev Early Oct [Re: cieldumort]
      #99694 - Tue Oct 02 2018 02:32 PM


GFS 240 Hrs out Valid 10-12-18 12Z. Image cr. Tropical Tidbits

Lots of opportunities for the developing gyre to spin out tropical cyclones, and this is being reflected in many model runs. Above is an example from today's 12Z GFS showing two concurrent depressions in the southwestern Atlantic on Friday the 12th. It is not clear in this run if either of these would qualify by NHC definition as a T.C. or not, but at ten days out, the signal is still clear.

Other runs of the GFS and other models, including "King Euro," have had similar results.

As a side note, it is also worth mentioning that the CMC had a major upgrade last month, and initial results are promising. Kudos to them, and it might be worth taking a second look at how that model handles this developing weather maker as well.


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cieldumortModerator
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Re: Possible Caribbean Dev Early Oct [Re: cieldumort]
      #99695 - Tue Oct 02 2018 04:52 PM



As can be seen in the image above courtesy Ryan Maue from Weathermodels.com, top globals including the ECMWF are becoming increasingly confident of a blocking pattern over the next few weeks, sending abundant moisture and perhaps several areas of interest (Invests) and/or TCs (official cyclones) into the GOM and/or southeast coast.

Areas at greatest risk may include but not be limited to: U.S. coastal states from Texas to Florida and points inland from there due to a risk of serious flooding, the Bahamas, the Yucatan peninsula, eastern mainland Mexico, Belize and Cuba.

As it looks increasingly likely that more than one significant disturbance or tropical cyclone will form in the SW Atlantic over the next two weeks, we will probably start individual threads assigned to specific individual Lows, with this thread pointing to them and back for reference.

The first disturbance that may be Invest tagged this week is a vigorous MCV located in the central Caribbean IsoFlame posts about above. Interestingly enough, this feature is partially associated with the remnants of former tropical storm Kirk (not enough to retain the name, however).


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cieldumortModerator
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Re: Central American Gyre [Re: cieldumort]
      #99696 - Wed Oct 03 2018 05:26 AM


Base satellite image courtesy Weathernerds.org IR 10-03-18-0830z

Quick predawn look at things...

An apparent developing gyre is centered roughly a few hundred miles north of Panama. A surface Low (denoted by a red "L") is located in the far eastern Pacific just west of northwestern Costa Rica. An apparent mid-level circulation (denoted by a yellow "MLC") is located south of Jamaica. Shear remains moderate to high north of 15N (and thus over the mid-level circulation).

It will be interesting to see if the East Pac surface low travels over or is otherwise absorbed into the western Caribbean side of the apparent gyre, which looks possible. At this hour it looks a bit healthier on the Pacific side than many models expected (it's kind of small, and small is often missed), which could have implications for inhibiting/delaying development in the W Caribbean, should it develop and stay over there.


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cieldumortModerator
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Re: Possible Caribbean Dev Early Oct [Re: IsoFlame]
      #99697 - Wed Oct 03 2018 12:15 PM

Visible imagery this morning shows a tiny, left-over LLC from the MCV that had some periods of robust convection over the past 36-48 hours or so, leaving behind the broader mid-level circ. As these two features are no longer stacked, and with the LLC heading west into the shear, development of this first disturbance looks less possible.

The EPAC surface Low to the west of northern Costa Rica continues establishing itself, and may have a better chance of genesis over the next 60 hours than the W Caribbean, although not yet outlined by NHC. Models have begun noticing and developing this feature.

Edit to add that based on high-res Visible though 1645z, the EPAC Low may be reforming to just off the southwest coast of CR, perhaps an indication that it is being drawn cyclonically in closer to the gyre center. There isn't much land to cross between the Pacific and Atlantic around there, if it were to do so. - Ciel

Edited by cieldumort (Wed Oct 03 2018 01:20 PM)


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cieldumortModerator
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Re: Central American Gyre [Re: cieldumort]
      #99698 - Thu Oct 04 2018 04:23 AM

Oct 4 0z model rundown sitll favors development of at least one system from this parent gyre.

NHC presently near 0% >48 hours, and 30% >120 hours.

ECMWF ensembles Implied Probability of Genesis in the NW Carib is now 80% within 120 hours.

There may be a trend in the models to work with the LLC being tracked in earlier posts. It has turned out so far to be a tenacious little bugger, still hanging on despite 40 KTS westerly shear. So it looks possible it may be our first CAG-related Invest after all (TBD).

ECMWF - Genesis by 0z Tues Oct 9 over the tip of the Yucatan Peninsula, becoming a 993 MB Tropical Storm in the north-central to northeastern Gulf next weekend.

GFS - 1st System: 998 MB tiny Trop Storm in the far East Pac landfalling on southern Guatemala by 6z Oct 9. 2nd System: Inverted Trof pushing inland into Louisiana on Wed Oct 10. 3rd System: New Tropical Low in central Caribbean by Oct 15.

GFS FV3 - 1st System: Genesis just offshore of Tampa, Fl by 06Z Oct 10 as a 1003 MB Trop Storm, making final landfall as a Cat 2 near Pensacola by 12Z Oct 12. 2nd System: 999 MB Trop Storm just south of Isthmus of Tehuantepec by 12Z Oct 16. 3rd System: 1005 MB Low nearing the Straits of Florida Oct 16.

CMC - Genesis just offshore of Belize by 0z Oct 7 as a 1003 MB TD, making final landfall as a Cat 1 near Mississippi/Alabama border 06Z Oct 12.

NAVY - Genesis between northern Yucatan and western Cuba by 0z Oct 8, making final landfall as a Cat 1 near Biloxi, Ms by 18Z Oct 10.

ICON - 1st System: 1007 MB TD forming just south of Guatemala by Oct 6, heading NW. 2nd System: Meager T.D. or Tropical Low forming south of Cuba by Oct 7, tracking north as a weak system to end of run on Oct 11 around the Straits of Florida.


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MikeCAdministrator
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Re: Central American Gyre [Re: cieldumort]
      #99699 - Thu Oct 04 2018 08:13 AM

Even thought the models are still quite mixed on this iarea, it does have strong support from the European ensembles.



Showing the various tracks. Odds are that if it develops it'll be a lopsided system with impacts on the east side only (ala Gordon) Shear in the W. Caribbean right now is still quite high. Time will tell though, if its in the Gulf in October it needs to be watched closely regardless.


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cieldumortModerator
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Re: Central American Gyre [Re: cieldumort]
      #99700 - Thu Oct 04 2018 01:57 PM

UKMET now also on board with development in the SW Atlantic
Quote:


NEW TROPICAL STORM FORECAST TO DEVELOP AFTER 102 HOURS
FORECAST POSITION AT T+102 : 22.3N 91.8W



This location would actually be in the southwest Gulf, roughly 180 miles northwest of Mérida, Yucatan

With the addition of UKMET, only the GFS is not doing much, after being somewhat bullish early on. That is not the case with the FV3-GFS, however, which is slated to replace the old GFS in 2019.


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Keith B
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Re: Central American Gyre [Re: cieldumort]
      #99701 - Thu Oct 04 2018 07:42 PM

At 8p, up to 50% in 5 days.

1. Surface observations and satellite data indicate that an area of low
pressure is located near Cabo Gracias a Dios on the eastern border
of Honduras and Nicaragua. This system is accompanied by an
extensive area of disturbed weather extending from Central America
eastward through Hispaniola. Upper-level winds are not currently
favorable for tropical cyclone formation, but environmental
conditions are forecast to become less hostile and a tropical
depression could form by late this weekend or early next week in the
northwestern Caribbean Sea or the southern Gulf of Mexico as the
system moves slowly northwestward. Regardless of tropical cyclone
formation, this disturbance will continue to bring torrential rains
primarily to portions of Central America and the Yucatan peninsula
during the next few days.
* Formation chance through 48 hours...low...near 10 percent.
* Formation chance through 5 days...medium...50 percent.

NHC

--------------------
Keith Boyer N4TRN
Orange County ARES
Asst. Emerg. Coord. (AEC) Skywarn Orange County, FL
http://www.ocares.org/


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cieldumortModerator
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Re: Central American Gyre [Re: cieldumort]
      #99702 - Fri Oct 05 2018 01:37 AM



The first disturbance born of this parent gyre to be Invest tagged has been the compact, nearly stationary Low centered off the northwest tip of Costa Rica, newly-"Invested" 97E.

Normally we would include EPAC systems in "Other Basins," but 97E is relevant to this thread in two ways. First, should 97E develop close to the coast (and thus close to the weak low in in the western Caribbean), it could siphon the life out of development potential there. Alternately, there is a small chance 97E gets drawn into the Caribbean. So we'll be watching it, mostly as it relates to development in the SW Atlantic, but also for its potential to produce very heavy rains and possibly flash floods over central America (separate thread if warranted just for that in "Other Basins.")


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cieldumortModerator
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Re: Central American Gyre [Re: cieldumort]
      #99703 - Fri Oct 05 2018 03:52 AM

Great reads Thursday about this particular CAG, and GAG-related TCs in general, on Wunderground and Weather.com

Wunderground: Gulf of Mexico Development Possible Next Week

TWC: Western Caribbean Is Hotspot for Tropical Development in October and Here's Why We're Watching It Now


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MikeCAdministrator
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Re: Central American Gyre [Re: cieldumort]
      #99704 - Fri Oct 05 2018 06:41 AM

No solid center still (and thus no invest), models are still a bit mixed, but the regular GFS is the only one showing no development. Many of the GFS ensemble members do show development, as does the FV3. Euro, CMC, and UkMet.

Landfall points range from Se Louisiana to the Florida Panhandle/ Some slow it offshore (Euro, CMC) with a brief loop before landfall in AL/FL Panhandle. The ones that do the loop don't have landfall until next weekend. Those that don't, like the UKMet, have a landfall in the Panhandle on Wednesday.

Without a decent center to go off of, it's difficult to pinpoint where it'll wind up, so the general idea is NE Gulf needs to watch it closely. Important to note that none of the models have it getting very strong.

Euro ensembles show what the lack of a decent center does to the models





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MikeCAdministrator
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Re: Central American Gyre [Re: MikeC]
      #99705 - Fri Oct 05 2018 09:26 AM

There's no invest yet, however the area is definitely interacting with the Invest 97E on the East Pacific side. For what it's worth.
97E (East Pacific Crossover?)


Although this too is unlikely to happen. It does highlight the lack of an organized area to use for the models, meaning it's too soon to tell what areas will be affected by this system.


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Re: Central American Gyre [Re: cieldumort]
      #99706 - Fri Oct 05 2018 01:19 PM

The operation GFS has joined the other models showing a system in the Northeast Gulf (La/Panhandle) area late next week. (cat 2)

12Z GFS Ensembles




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cieldumortModerator
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Re: Central American Gyre [Re: cieldumort]
      #99708 - Fri Oct 05 2018 02:36 PM

In addition to the Low centered in the EPAC (97E), the broader low center in the northwest Caribbean has now also been Invest-tagged, 91L, and we have set up a Lounge specific to it: 91L Forecast Lounge

This is the primary disturbance models have been homing in on for development near the Yucatan or in the Gulf during the next 7 days.


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