Talking the Tropics w/ Mike: Helene inland... Isaac N. Atlantic... Joyce forms... eye on Caribbean

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Tropics threats for Jacksonville/NE Florida/SE Georgia: Helene moving farther inland allowing winds to diminish through the day Friday.

“Buresh Bottom Line”:

* Major impacts from Helene will continue well into Georgia, Tennessee & the Carolina’s as Helene weakens inland but still produces heavy rain & major flooding along with tornadoes. ***

* Isaac & a strong tropical wave over the Eastern Atlantic will stay far to the east over the open Atlantic

* Tropical storm “Joyce” has formed over the E. Atlantic but will not make it very far across the Atlantic.

* Eye on potential longer range tropical development over or near the Caribbean & Gulf of Mexico

The Atlantic Basin Overview:

(1) “Helene” -

As expected... “Helene” formed over the Northwest Caribbean... was upgraded to a tropical storm Tue. morning & a hurricane Wed. morning undergoing a rapid intensification cycle Thu. afternoon taking the hurricane to a Cat. 4 with a landfall about 11:10pm 10 miles W/SW of Perry in the Big Bend. The most U.S. hurricane landfalls in a season is 7 in 1886 followed by 6 in 2004 & 2020... the number stands at 4 through Sept., 2024.

According to Dr. Phil Klotzbach, Helene is the strongest hurricane to ever hit the Big Bend...the 4th Gulf Coast landfalling hurricane this year which has only happened 5 other times since 1851... lowest central pressure for a landfalling hurricane in Florida since Michael in 2018 (Cat. 5)... 9th strongest hurricane since 1900 to make landfall in Florida (based on sea level pressure).

The trek northward is being caused by general troughing aloft over the Lower 48 that is being strengthened by a deep upper level disturbance dropping southward into the heart of the U.S. that will then cut off from jet stream while capturing Helene. The trough is drawing Helene N/NW then northwest before stalling & weakening further over the Tennessee Valley & Appalachians once in the “belly” of the upper trough. The combination of the stalled upper trough & then Helene remnants will result in an extreme rainfall event for parts of the Tennessee Valley, Lower Ohio Valley & Southern Appalachians.

The Caribbean & Gulf are a climatologically favored area for tropical development later in Sept./Oct. & such systems are often steered northward by an ever more active, more meridional jet stream as we start to see the impacts of autumn weather patterns. The water, of course, is very warm & deep oceanic heat content is just about at its annual peak.

Helene at the Big Bend is the 3rd (Idalia & Debby) hurricane landfall in the last 13 months - a very rare feat.

It was interesting - as I noted the last few days - the rapid strengthening of hurricane “John” over the far East Pacific earlier in the week that moved inland on the west (Pacific side) coast of Mexico Mon. night/early Tue. while Helene was just trying to get its act together. There may have been some symmetry with the Gulf system as upward vertical velocities that aided John spread eastward to the Atlantic Basin.

Keep in mind impacts from the storm will extend well beyond the center AND the cone. Do not fixate on the cone or a perceived center point. Remember that a skinny cone simply means a higher confidence forecast & that dangerous weather conditions will extend way beyond the cone:

Heavy rain is forecast along much of the Gulf coast. While it’s recently been drier for NE Fl. & SE Ga., a lot of water remains “in the system” so flooding will be a concern by Thu./Fri.:

(2) “Isaac” formed Wed. evening, Sept. 25th over the North Atlantic & has become a hurricane but is no threat to land. The avg. date for the 9th named Atlantic storm is Sept. 16th... the avg. date for the 6th Atlantic hurricane of the season is not until Oct. 15th.

(3) A strong tropical wave over the Eastern Atlantic was upgraded to tropical storm Joyce Fri. morning. The 10th Atlantic named storm develops on average Sept. 22. Joyce will not have a very long life span as hostile conditions will be encountered by Sunday over the Central Atlantic followed by dissipation by at least early to mid next week while turning sharply northward. No threat to any land areas.

Another tropical wave is following coming off the coast of Africa with potential development.

(4) Low pressure is again forecast to form over the Western Caribbean with potential tropical development in the longer term - roughly in the period Oct. 5 - 10th. For the moment - as one would expect beyond 5-7 days - forecast models are showing many mixed signals. Suffice to say at this point the area will need to be closely monitored.

Climavision’s HorizonAI Global Model (this model uses its own data & analysis for initialization of each model run + some AI input) valid for late Fri., Oct. 4th:

‘Velocity potential anomalies’ below shows far less “sinking” air (brown lines) across the Atlantic Basin. With sinking air, tropical development can occur but overall conditions are not as conducive as when there is overall rising (green lines) air where convection is active. This “pulse” of upward motion has moving eastward & may be helping the active period of tropical activity across the Atlantic into October.

REMEMBER WHEN A TROPICAL STORM OR HURRICANE IS APPROACHING: Taping windows is *not* recommended & will not keep glass from breaking. Instead close curtains & blinds.

Realize the forecast cone (”cone of uncertainty”) is the average forecast error over a given time - out to 5 days - & *does not* indicate the width of the storm &/or where damage might occur.

The upper oceanic heat content (UOHC) [tropical cyclone heat potential/TCHP] across the SW Atlantic, Gulf & Caribbean is very high:

Water vapor loop (dark blue/yellow is dry mid & upper level air):

September tropical cyclone origins (early season breeding grounds are the Gulf &/or Western Caribbean:

Averages below based on climatology for the Atlantic Basin for September (2 hurricane so far, 3 tropical storms):

Wind shear (red - strong shear; green - low shear):

Saharan dust spreads west each year from Africa driven by the prevailing winds (from east to west over the Atlantic). Dry air = yellow/orange/red/pink. Widespread dust is indicative of dry air that *can* interfere with the development of tropical cyclones. However, sometimes “wanna’ be” waves will just wait until they get to the other side of - or away from - the dust plume then try to develop if other conditions are favorable (we’ve already seen this with Beryl & Debby this year). In my personal opinion, there is way too much “hoopla” about the presence of Saharan dust & how it relates to tropical cyclones. In any case, the peak of Saharan dust typically is in June & July.

2024 names..... “Joyce” 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 (the last time this year’s list was used)... Dorian in ’19 & Laura, Eta & Iota in ‘20, Ida in ‘21 & Fiona & Ian in ‘22]). In fact, this year’s list of names is rather infamous because of the ‘04 season when Charley, Frances, Jeanne & Ivan - all retired names - hit Florida within a matter of about 6 weeks. 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 three times - 2005, 2020 & 2021). The naming of tropical cyclones began on a consistent basis in 1953. More on the history of naming tropical cyclones * here *.

Peak of the hurricane season Sept. 10th:

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 over the Gulf, Caribbean & deep tropical Atlantic. The colors will brighten greatly as the water warms to greater depths deeper into the season: