Talking the Tropics With Mike: Isaias on track to reach Florida Sat. night/Sunday

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*** Low pressure/tropical wave ’92-L’/‘Potential Cyclone Nine’ was upgraded to tropical storm Isaias Wed. evening while over the Eastern Caribbean.... moved over Eastern Dominican Republic Thu. afternoon then offshore & quickly reorganized becoming the 2nd hurricane of the Atlantic season a little before midnight. Isaias is the 5th July named storm over the Atlantic which ties the record for the month set in 2005. It marks the fastest to ‘I’ beating the previous record set by “Irene” in - when else - 2005.


Indications are that Isaias will now fairly steadily strengthen into Sat. while moving northwest then more northward but not before reaching the southeast coast of Florida Sat. night/early Sunday followed by a track anywhere from ~40-70 miles east of NE Fl./SE Ga. with the closest approach Sunday night into Mon. morning. On this track, impacts locally - which *do not* appear severe - for Jax/NE Fl./SE Ga - subject to change!:

-- bands of heavy rain north & northwest of the center Sunday/Sunday night. Amounts ranging from 1-2″, locally more near the coast to a half inch or less west of I-95

-- a dangerous rip current risk at area beaches with rough seas & surf. The best advice is to stay out of the ocean over the weekend... ships & boats should stay in port.

-- storm surge of approximately 2-4 feet possible for St. Johns County coastal areas... lesser surge to the north but still possibly up to 3 feet in places, especially if closest approach coincides with high tide &/or very heavy rainfall.

-- an isolated waterspout &/or tornado Sunday/Sun. night.

-- breezy winds of 15-25 mph, gusts 30+ mph at the beaches... 10-20 mph along I-95... much lighter inland west of I-95. Right now I am *not* forecasting sustained winds of 40+ mph which would close down area bridges.

-- overall - as long as the forecast track is accurate - impacts to NE Fl./SE Ga. should be minor & most significant at area beaches. Electrical & business infrastructure should stay intact & operational through & after the closest passage of Isaias. However, one should always respect mother nature & its forces so take this storm & its impacts seriously without “going over the edge”(!).

Isaias remained reasonably well organized after traversing the rugged terrain of the Dominican Republic Thu. missing some of the highest mountainous peaks. Moving at more than 20 mph, Isaias did not stay over land for much more than 8-10 hours. The overall structure of Isaias remains somewhat ragged & asymmetrical, but aircraft recon is showing better organization & the presence of a more defined eye at times. The western circulation quadrant appears to be a little less restricted though is still suffering from shear out of the west/southwest. There is very warm ocean water ahead (Gulf Stream). Isaias is still having to battle occasional intrusions of dry air as evident Fri. evening as a swath of dry air moved northeast from Cuba.

So the atmospheric environment for Isaias is somewhat marginal while water conditions are rather optimal. All things considered, this would appear to be rather compact hurricane near landfall on the Fl. coast followed by slow weakening while turning more north.

Forecast models have generally started to converge on a solution that takes Isaias very near to - if not into - SE Flordai close to West Palm Beach Sat. night/early Sunday then a turn north/northeast to east of Jacksonville.... to very near the Carolina’s Monday night then to near New England Tue. night as the storm accelerates northeast. The expectation is for environmental conditions do be favorable enough for Isaias to maintain hurricane strength thanks to warm sea surface temps., proximity to the very warm Gulf stream & possibly some upper level help from an approaching trough before land interaction Sat. night.

Overall forecast models recently have generally trended north but also more west. There is a good deal of shear (12th image below) in the vicinity of Isaias - on the order of 25-30+ mph - but the shear decreases briefly the more north & west it goes until shear starts to increase due to an approaching upper level trough. There is also some dry air (13th image below) that will likely occasionally infiltrate the system.

There is an alleyway of sorts developing near the U.S. east coast/far W. Atlantic. A more organized Isaias seems to now be sniffing out that alley lending confidence to the more north solution in the long run. The approaching upper level trough moving into the Eastern U.S. should help eventually steer Isaias north then northeast. The trough may help with the upper level ventilation of the storm negating some of the effects of potential low level shear. However, it looks there will also be land interaction over the weekend. The GFS model is still a little east of the operational European & UKMET models. The GFS remains decidedly faster (by 10+ hours) than either the European or UKMET models. A compromise between all three is the prudent route at this juncture & probably will end up closest to reality. Of note... the UKMET showing a ricochet-effect by sort of “bouncing” Isaias off the SE coast of Fl. then abruptly turning N/NE. The combination of frictional effects from land + the approaching trough make such an outcome at least somewhat plausible. Either way, the center of Isaias looks to stay east of Jacksonville in the long run & if not.... the tropical cyclone will be over land for a longer period of time before reaching Jacksonville’s latitude causing significant weakening & thereby not likely increasing the impacts much more than currently forecast (at the top of this blog) given either scenario. A more west track would bring more rain to the area, but there is not a whole lot of extra water in the “system” (intracoastal, estuaries, canals, creeks, etc), so we can at least some heavy rain. (vs. Matthew & Irma when our ground was far more saturated).

Radar imagery below with forecast track of Isaias courtesy S. Fl. Water Management District:

Westward shift in the model spaghetti plots:

Current shear:

Dry air:

As for rainfall... there is the potential for some pretty decent banding of rain north & northwest of the center as “Isaias” approaches NE Fl./SE Ga. The combination of strong onshore flow (winds out of the east), surface convergence & friction should develop enough banding to produce as much as 1-2″+ of rain close to the coast. These bands will be capable of producing wind gusts of 30+ mph as well as isolated waterspouts/tornadoes with most of the rain falling between noon Sunday & noon Monday.

Projected path of Isaias in red vs. Floyd, 1999/Matthew, 2016/Dorian, 2019. It should be noted that Floyd, Matthew & Dorian were considerably stronger & larger tropical cyclones....

Meanwhile... a tropical wave has some potential to develop some over the Central Atlantic while moving northwest. And t.d. #10 has formed just off the coast of Africa over the far E. Atlantic, but the depression should fall apart Sat. night/Sunday then dissipate.

Atlantic dust continues to spill west off of the Saharan desert over the E. Atlantic. Tropical waves continue to “fester” along the south edge of the dust & have the potential to thrive once away from the dust.

2020 names..... “Josephine” is next on the Atlantic list (names are picked at random by the World Meteorological Organization... repeat every 6 years... historic storms are retired (Florence & Michael last year) & Dorian is certain to be retired from the ’19 list....

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 extreme over the NW 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: