Talking the Tropics With Mike: Weak tropical systems will give way to stronger Sam over E. Atlantic

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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”:

Both weak tropical cyclones continue to struggle & should eventually dissipate, open up into a trough of low pressure &/or become post-tropical. The overall environment - pockets of strong shear + some dry air - will ultimately rule the day. Also important - the positioning & strength of the Bermuda High in tandem with a fairly constant upper level trough over or near the U.S. east coast. At this point, it seems any systems over the next week to 10 days will struggle to make it too far west within a the somewhat marginal environment (which includes “sinking air” too) in addition to an alleyway (weakness/trough of low pressure) over the Western Atlantic that remains in place - a sort of U.S. “protector” - at least for the east coast.

Peter is moving more northwest though the low level swirl that is the “center” has had a tendency to drift more west probably due to its shallow nature. A turn more northward should occur the next few days.... keeping Peter north of the Caribbean & Windward Islands.

Meanwhile... Rose over the far Eastern Atlantic & should will move much more north than west & is of no concern for any land areas while weakening later in the week.

In the satellite era, only 2005 and 2020 have had the seventeenth named storm on an earlier date than Sept. 19th.

And “Odette” may try 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 end of the week, the storm will again get forced northeast over the open N. Atlantic & will lose any subtropical characteristics that might have been regained over the next few days.

Meanwhile... another strong tropical wave - ‘98-L’ has marched westward off the coast of Africa but at a lower (more south) latitude than recent waves. ‘98-L’ should strengthen over time & become a named storm. 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 to 10 days. 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 anything but a sure thing. The European is just about due west to slightly northwest on a march to the Caribbean while the GFS is indicating a sharp turn north & out over open water well before the Caribbean. Stay tuned....

Wave ‘98-L’:

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 which will help turn Atlantic tropical systems more northward before getting very far west.

And an unfavorable MJO phase should keep Atlantic tropical cyclones mostly “in check”. 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* 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..... “Sam” 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:


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: