Weather

Talking the Tropics With Mike: T.D. #18 becomes Sam

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REMEMBER WHEN A TROPICAL STORM OR HURRICANE IS APPROACHING: Taping windows is *NOT* helpful & will not keep glass from breaking... & realize the cone is the average forecast error over a given time - out to 5 days - & *does not* indicate the width of the storm &/or damage therefore do not become fixated on the center of a tropical system.

“Peter” & “Rose”:

The last NHC advisory has been issued on both systems & no re-generation is expected.

“Odette”: trying to make a bit of a comeback over the NW Atlantic as the post-tropical cyclone turns more southeast & moves over warmer water again which could help the cyclone become subtropical while remaining over the open N. Atlantic. By the weekend, the storm will encounter strong shear & should begin to weaken again.

Meanwhile... the strong tropical wave - ‘98-L’ - was upgraded Wed. afternoon to tropical depression #18 then to tropical storm “Sam” Thursday morning while marching westward at a lower (more south) latitude than recent waves. Sam should strengthen over time & become a hurricane rather quickly. The jury is still out on how far west this one might make it but heads up for parts of the Caribbean in a week or so. It *might* still be a little early on the re-orientation of the steering currents to bring this wave real far to the west, but it’s not a sure thing. The European is just about due west to slightly northwest on a march to & near the Northeast Caribbean while the GFS is indicating a sharp turn north & out over open water well before the Caribbean. More recent European operational model runs have started to trend northward in the direction of the GFS. The end result will be driven by the recent readjustment of the upper level flow across the Northern Hemisphere which includes a pretty persistent trough over & near the Eastern U.S. & Western Atlantic. If the trough stays, the U.S. eastern seaboard is protected with the question being will t.d. #18 stay far enough south so as to not be drawn northward in the well established alleyway that has recently kept tropical systems well to the east over the open Atlantic. The GFS model has ruled the hurricane season so far so a nod - for the moment - on turn more northward in time. But this will be one to carefully watch/monitor so stay tuned....

This is the 2nd earliest formation of the 18th named storm in the Atlantic basin, moving ahead of the infamous 2005 hurricane season, and only trailing last year.

According to Phil Klotzbach: * Only 1 season on record has had 18+ Atlantic named storms by 23 September: 2020 with 23 named storms by 23 September.

* And Sam is the 13th Atlantic named storm to form in the Atlantic since 11 August. Only 2020 has had more Atlantic named storm formations between 11 August - 23 September with 14.

Elsewhere: another African tropical wave will emerge off the coast of Africa & has the potential for long range development as the wave moves west or W/NW.

And low pressure may also try to form near or east of the Bahamas along a stalled front through the weekend into early next week. Any tropical or subtropical development would be slow to occur with *current* indications that the system would stay east of Florida & the U.S. east coast.

Sam spaghetti plots:

The Bermuda High looks to stay displaced well to the north & east over the Atlantic while a sharp upper level trough moves into the Eastern U.S. Such a set-up should allow for the alleyway to remain over the Western Atlantic for the time being.... *possibly* through much of next week.

And an unfavorable MJO phase is helping keep recent Atlantic tropical cyclones mostly “in check”, but that’s about to change. There is a lot of “sinking” (brown lines) air over the Atlantic Basin which doesn’t usually favor strong hurricanes (there can be exceptions!). *But* the rising air (green lines) will likely overspread the Atlantic by Oct.

Related to the above discussion - a period of heightened concern for U.S. impacts will evolve toward the end of the month & especially into Oct. - more on that potential *here* in the “Buresh Blog”.

Ocean temps. remain “fit” to help maintain tropical cyclones.

Sea surface temps. across the Atlantic are now near to above avg. across much of the basin (2nd image below) & - even more importantly - deep oceanic heat content (which helped “feed” Ida) is impressive & the “equivalent oceanic heat content” - namely depth averaged temperature in the upper 300 m (~984 feet) - is even more impressive all the way from Africa to the Gulf of Mexico. Such an ocean water temp. pattern is conducive to long track deep tropical Atlantic tropical cyclones & can lead to a more favored regime for rapid intensification cycles. From an AMS research paper in ‘08 Mainelli, DeMaria, Shay, Goni: “Results show that for a large sample of Atlantic storms, the OHC variations have a small but positive impact on the intensity forecasts. However, for intense storms, the effect of the OHC is much more significant, suggestive of its importance on rapid intensification. The OHC input improved the average intensity errors of the SHIPS forecasts by up to 5% for all cases from the category 5 storms, and up to 20% for individual storms, with the maximum improvement for the 72–96-h forecasts. The statistical results obtained indicate that the OHC only becomes important when it has values much larger than that required to support a tropical cyclone.” More recent research continues to indicate similar correlations.


Saharan dust. Dry air - yellow/orange/red/pink. Widespread dust is indicative of dry air that can impede the development of tropical cyclones. However, sometimes “wanna’ be” waves will just wait until they get to the other side of the plume then try to develop if everything else happens to be favorable. In my personal opinion, way too much is made about the presence of Saharan dust & how it relates to tropical cyclones.

2021 names..... “Teresa” is the next 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 in ’19 & Laura, Eta & Iota in ‘20). Last year - 2020 - had a record 30 named storms. The WMO decided beginning in 2021 that the Greek alphabet will be no longer used & instead there will be a supplemental list of names if the first list is exhausted (has only happened twice - 2005 & 2020). More on the history of naming tropical cyclones * here *.

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 continues to increase across the Gulf, Caribbean & deep tropical Atlantic & has become pretty impressive from the Central/NW Caribbean into the Gulf of Mexico:

Sea surface temp. anomalies:

SE U.S. surface map:

Surface analysis centered on the tropical Atlantic:

Surface analysis of the Gulf:

Caribbean:

GFS wave forecast at 48 & 72 hours (2 & 3 days):

Atlantic Basin wave period forecast for 24, 48 & 72 hours respectively:

The East Pacific:

West Pacific IR satellite:

Global tropical activity: