Talking the Tropics With Mike: Franklin over Caribbean... Gert forms... Hilary flooding California

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Over the Atlantic:

Overall... conditions over the Atlantic Basin are relatively hostile right now despite all the “action” (a number of tropical waves & named systems). Wind shear is rather strong & the mid & upper level moisture is inconsistent & rather dry across a good part of the Central Atlantic. The tropical cyclone of greatest concern is Franklin since it will impact Haiti & the Dominican Republic soon with very heavy rain. Another concern will be ‘91-L’ moving west across the Gulf of Mexico potentially bringing gusty winds & heavy rain to parts of South Texas as the system strengthens all the way up to landfall.

(1) the “lead” tropical wave ‘90-L’ is now tropical storm “Franklin” over the Eastern Caribbean. Westerly wind shear will be quite strong over the next several days but a turn in the forward movement to the north then N/NE may help mitigate some of the shear. Furthermore...the shear should weaken by mid to late week. Franklin will turn rather sharply to the north late Mon./early Tue. moving over or at least very near Hispaniola Tue./Wed. where a tropical storm WATCH has been issued. Land interaction at midweek with the mountainous terrain of Hispaniola should cause at least some weakening but conditions appear favorable for intensification once north of the islands as long as the core of Franklin is not too badly degraded. There is some question in the longer range - next weekend & beyond - on whether or not Franklin will get fully captured by a series of troughs to the north or eventually left behind. The initial trend will be northeast once over the SW Atlantic, but we’ll need to keep a close eye on how steering currents evolve & how strong & how far south the troughs will be.

In the meantime, heavy & gusty rain squalls will impact Puerto Rico & nearby islands followed by very heavy rain & gusty winds centered on Haiti & Dominican Republic Tue./Wed.

A Tropical Storm WATCH: * Haiti entire south coast from Anse d’Hainault eastward to the Dominican Republic border....* Dominican Republic entire south coast from Haiti border eastward to Isla Saona.

(2) ‘99-L′ - over the Central Atlantic & east of the Caribbean become tropical depression #6 & then was upgraded to tropical storm “Gert” about midnight early Monday by the NHC due satellite derived estimated winds near a very brief burst of convection. Conditions - dry air & wind shear - are not favorable so further strengthening is unlikely. Gert is still expected to dissipate well east to the Windward Islands (Caribbean) within the next 24 hours or so.

(3) ‘98-L′ was upgraded to tropical storm “Emily” Sun. morning over the Eastern Atlantic after coming off the coast of Africa last Wed. Emily will turn more northward relatively early over the open Central Atlantic & far away from any land areas while also weakening as shear increases markedly. There may be some long range re-strengthening over the N. Atlantic if Emily can survive the hostile conditions in the coming days.

(4) a tropical wave - ‘91-L’ is moving away from Fl., & has organized some over the Eastern Gulf of Mexico. Its swift movement to the west is one of the more significant negative aspects for ‘91-L’ in an otherwise increasingly favorable environment, but the wave may still become a depression or even a tropical storm before reaching the South Texas coast by Tue. Heavy rain & gusty winds are becoming more likely for South Texas. The movement is pretty straight forward for 91-L thanks to a persistent & strong upper level high centered over the middle of the U.S. (causing a Midwest heat wave).

(5) another strong tropical wave has just come off the coast of Africa. This wave may very well develop but appears destined to stay far out to the east over the Atlantic.

Right now the Bermuda high at the surface is displaced rather far to the east/northeast over the Atlantic... while a strong upper level ridge of high pressure is parked over the Central U.S. This pattern should more or less hold for at least the next 5-6 days. This set-up is helping to preserve the alleyway over the W. Atlantic... at least for this week.

500mb (~30,000 feet) GFS forecast for Wed., 08/23 (note the well defined alleyway over W. Atlantic):

GFS surface forecast for Wed., 08/23:

Check out the upper oceanic heat content (UOHC) [tropical cyclone heat potential/TCHP] across the SW Atlantic, Gulf & Caribbean. The warmth is very deep. But keep in mind warm ocean temps. alone doesn’t necessarily equate to a “big” hurricane season (need other ingredients & factors to be favorable too):

In the East Pacific... once powerful “Hilary” made landfall on the west & northwest coast of the Baja of California early Sunday afternoon & is quickly weakening. While not arriving in California as a hurricane, Hilary will *still be a major blow* for parts of the SW U.S., especially in the form of flooding rains. So though much weaker (cooler water temps. + land interaction + shear) while moving to the south coast of California, there will be a strong surge of tropical moisture northward into California, parts of Arizona, Utah & Nevada that is causing heavy rain & flash flooding with some desert areas potentially receiving as much as a year’s worth of rain over just a couple of days. There will also be very rough seas & surf along the coast of Southern & SW California. Winds for California & Western Arizona & parts of Nevada will average 30-50 mph but with gusts to 60+ mph. Orographic influences will cause narrow corridors of stronger winds.

A tropical storm WARNING continues from the California/Mexico border to Point Mugu, Catalina Island.

The center or core of Hilary is moving rapidly having passed just east of San Diego Sun. afternoon & crossing into Nevada early Monday. While at least somewhat similar storms have happened before, it is rare. Tropical storm “Kathleen” in 1976 brought very heavy rain to parts of California & a tropical storm in 1939 also brought very heavy rain & flooding to parts of California. Interestingly - & not likely coincidentally - both were during El Nino years (weak in ‘76 but strong in ‘39).

As is typical with landfall tropical cyclones, the underside (south) of Hilary has been abruptly eaten away by dry continental dry air wrapping around the circulation. The result will be a quick decrease in the heaviest rain once the center passes any single location. In the end, the heaviest rainfall amounts will average 3-6″+ with amounts in some of the higher elevations more than twice that.

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

July tropical cyclone origins:

Averages below based on climatology for the Atlantic Basin for August:

Wind shear:

Saharan dust spreads west each year from Africa 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 impede 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 plume then try to develop if other conditions are favorable. In my personal opinion, way too much is made 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.

2023 names..... “Harold” 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, Ida in ‘21 & Fiona & Ian in ‘22]). In fact, this year’s list of names is rather infamous with “Katrina”, “Rita” & “Wilma” retired from the ‘05 list & “Harvey”, “Irma”,“Maria” & “Nate” from the ‘17 list. 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 *.

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 brighter colors are expanding dramatically as we near the peak of the hurricane season.: