Talking the Tropics With Mike: T.D. #26 strengthens into tropical storm Delta

Headed for the U.S. Gulf coast by late week

Talking the Tropics With Mike: T.D. #26 strengthens into tropical storm Delta

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Overall... the Caribbean & Gulf of Mexico continue to be areas to watch for at least the next couple weeks... along with nearby areas of the SW Atlantic. If traveling anytime soon to any areas susceptible to tropical systems, stay up to date on the latest, updated forecast......

A Caribbean tropical wave was upgraded to tropical depression #26 Sun. night & to tropical storm “Delta” (not like Delta Dawn!, bow to Helen Reddy) early Monday while moving west/NW across the Caribbean a little south & southwest of Jamaica. Like has happened so often this season, this is the fastest ever to the 25th storm beating by more than a month the previous record of Nov. 15th, 2005. Models had been wildly inconsistent amongst themselves not to mention compared to one another until starting to smooth out later Sunday followed by remarkable agreement by early Mon. While there may be some initial interaction with a weakening Gamma to the northwest over/near the Yucatan Peninsula, it looks Delta becomes the dominant one & rules the day. The west/northwest movement will become more northwest through mid week then turning more north, even northeast late in the week as a new upper level trough digs into the Lower 48 weakening the upper level ridge across the Northern Gulf. This upper level trough - timing, orientation & strength - will be a major player on where the tropical cyclone (Delta) goes & how strong it might be. Given recent trends & typical model biases, it seems a more westward position for a longer period of time might be the way to go which would put Delta close to the Yucatan Peninsula or even Belize for turning more northward.

In any case.... anyone with travel plan to the west along/near the Gulf Coast should stay up to date on the latest forecasts for Delta.

Currently there is a good deal of shear over the Gulf of Mexico on the order of 30+ mph that only becomes stronger the more north over the Gulf. This shear will essentially remain in place for the next few days before lessening by the weekend/the following week. By then, Gamma may be a thing of the past as the storm has been hammered (mid & low level centers decapitated) by the strong shear out of the southwest. There is also nearby dry mid & upper level air. So it seems the harsh environment will rule the day with regards to Gamma but Delta may be far enough removed from the harsh environment to not only survive but thrive, especially in the short term. By the time Delta is into the Northern Gulf, the shear should be relaxing some & will also be in the direction from which Delta is moving which may mean a little less impact on the storm.

A word of caution!: the models have struggled with the pattern recently & the upper level steering currents will be evolving considerably in the coming days thanks to the “new” trough moving into the U.S.

Meanwhile.... Tropical depression #25 formed over the Western Caribbean Fri. morning & strengthened into tropical storm “Gamma” Fri. evening & would have reached hurricane strength Sat. had it not been for landfall on the Yucatan Peninsula about 1pm EDT. It’s the fastest ever to the 24th tropical storm of the season beating the record of Oct. 27, 2005.

The combination of a tropical wave, lower pressures & an old front developed low pressure at the surface over the far Western Caribbean which was upgraded Fri. to t.d. #25 then tropical storm Gamma Fri. evening. The GFS model has been superior so far indicating a more northward move over the weekend. Most models now seem to be catching on. Despite the northward move into the warm water of the far Southern Gulf, Gamma is now dominated by high shear that will not change much in the coming days. The shear (out of the southwest) is very evident on satellite imagery as the center is well southwest of the strong convection. Therefore - despite an uptick in intensity Sunday for a while - Gamma is likely to weaken as it moves west/southwest across the far Southern/SW Gulf & eventually again near the coast of Yucatan. If Gamma survives the hostile conditions & land interaction, there’s some potential for “rejuvenation” over the Western Gulf late in the week & over the upcoming weekend but that scenario appears unlikely as Gamma gets driven farther south into Mexico thanks to a combination of a building ridge to its northwest & the large circulation of strengthening Delta to its east & eventually northeast.

As I mentioned last week, dominant high pressure across northern latitudes this time of year often does yield tropical trouble that begins in or near the Caribbean. Personally I would be surprised if there was not at least one Cat. 3+ hurricane that develops out of this pattern even though the forecast models are not indicating such for the moment. I don’t type this to try to “cry wolf” - it’s my job to forecast. Hopefully whatever does develop does not end being a major landfalling storm. In any case... stay tuned!

Other tropical waves farther east will have a hard time making it all the way across the Atlantic & will be encountering increasing shear - typical later in the season.

Water vapor imagery clearly shows the dry mid & upper level air across the NW Gulf as well as over Cuba which could have some impact on Delta:

Persistent, broad & strong high pressure at northern latitudes helping to induce low pressure at lower latitudes:

Through at least mid month.... vertical velocities look to become more favorable across the Atlantic Basin Oct. 10-20 - “ish”. “Velocity Potential Anomalies” show a good deal of sinking air (brown lines) right now but more favorable rising air (green lines) should push east from the Pacific in due time which does match a climatological 2nd peak of sorts (Oct. 15-20) for Atlantic tropical development.

October tropical cyclone origin points are clustered over the Caribbean, Gulf of Mexico & SW Atlantic:

Atlantic Basin wave forecast for 24, 48 & 72 hours respectively (major wave action at Fl./Ga. beaches through early next week due to persistent brisk onshore flow (high pressure to the north) combined with easterly swells from distant Teddy:

Saharan dust:

2020 names..... “Wilfred” was the last name on the Atlantic list (names are picked at random by the World Meteorological Organization... repeat every 6 years... historic storms are retired (Florence & Michael in ’18 & Dorian is certain to be retired from the ’19 list). Interesting side note: the last six of the names on the ’20 list had never been used. So it’s on to the Greek alphabet now. “Epsilon” is next... the first time the Greek alphabet has been used since 2005 (total of 27 named storms using 6 Greek letter names in ’05)

East Atlantic:

Mid & upper level wind shear (enemy of tropical cyclones) analysis (CIMMS). The red lines indicate strong shear:

Water vapor imagery (dark blue indicates dry air):

Deep oceanic heat content is impressive across the SW Atlantic, Gulf of Mexico & especially the Caribbean:

Sea surface temp. anomalies:

SE U.S. surface map:

Surface analysis centered on the tropical Atlantic:

Surface analysis of the Gulf:


Global tropical activity:

Marie” is quickly weakening now over the open waters of the E. Pacific: