Talking the Tropics With Mike: Tropical storm Isaias trying to organize & strengthen

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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 - still unclear exactly how this scenario will unfold but some impacts to Fl. are possible over the weekend into early next week - stay up to date. 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 the system will be near or east of Fl. by the weekend/early next week but - as it looks right now - not particularly strong. If true, primary local impacts for Jacksonville/NE Fl./SE Ga. would be heavy rain & perhaps gusty winds along with rip currents at area beaches along with rough seas & surf. All, of course, predicated on the exact location & strength. If Isaias manages to stay east of Florida, the storm will likely be stronger but with greatest impacts offshore. If farther west, land interaction would result in a weaker system but with more impacts, especially heavy rain. ***

I cannot emphasize enough there will continue to be changes to the track, intensity & impacts. But now that a center has formed, there’s a better chance for more forecast consistency.

The ultimate track will likely hinge on two things:

(1) the Bermuda high to the north which is broad & strong.

(2) intensity. Weaker - more west with a slower turn more northward as has been the case the last several days.... stronger - more north. It looks like a portion of Haiti, possibly the Dominican Republic will interfere with Isaias’s circulation through Thu. night. The terrain of Hispaniola is very mountainous with peaks well above 5,000 feet. A direct passage over the island will likely seriously disrupt the system. The interaction may also cause a new center to form or a “jump” of the center to a little north of the island.

The poorly defined center will likely jump around some until & unless it can become consistently couched under the strong convection. Isaias should slow as it nears the edge of the upper level ridge through Fri. There will be a move over parts of Haiti &/or the Dominican Republic Thu. afternoon & evening. We’ll have to see what kind of shape the center is in once north of Hispaniola which will help dictate reorganization & intensification.

Forecast models have generally started to converge on a solution that takes Isaias to the SW Atlantic & Bahamas then near or east of Fl. to very near the Carolina’s.

The European model seems to have settled on bringing a moderate tropical cyclone to near S. Florida then near or over Fl. over the weekend but the operational model has been jumping around a good bit from one forecast cycle to the next... the GFS has been & remains generally more east in the long run... & the UKMET is between the two but has trended toward the European with a weaker tropical cyclone (had been indicating a strong hurricane at times) in the vicinity of Fl. by the weekend before moving offshore of Jacksonville & trying to restrengthen.

Overall forecast models recently have generally trended north & east & still insist on the northward move which is more realistic now that there is a center & the system - as a whole - is “deeper”. There is a good deal of shear (6th image below) in the vicinity of the wave now - on the order of 25-30+ mph - but the shear decreases the more north & west it goes (until shear increases some late in the weekend/early next week due to an approaching upper level trough). There is also some dry air (7th image below) that may occasionally infiltrate the system as it organizes.

There does seem to be an alleyway of sorts developing near the U.S. east coast/far W. Atlantic. A more organized Isaias may now be sniffing out that alley lending confidence to the more north & east solution in the long run. The approaching upper level trough moving into the Eastern U.S. should eventually steer Isaias north then northeast. The trough may help with the upper level ventilation of the storm while along or near the east coast & Isaias may undergo a period of fairly “solid” intensification early next week as indicated by some models.

Current shear:

Dry air:

As for rainfall... the European is heaviest since the operational run is more west. The GFS model is far less given its forecast track to the east.

Tropical waves continue to move west off Africa but conditions are not particularly favorable for development at the moment but will need to be monitored, of course.

E. Atlantic tropical wave/disturbance spaghetti plots:

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 of which there is plenty across most of the Atlantic at the moment:

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: