Talking the Tropics With Mike: Hanna well inland & weakening... all eyes on strong Atlantic tropical wave

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(1) the tropical wave/disturbance that’s been moving northwest across the Gulf of Mexico strengthened into tropical depression #8 Wed. evening & tropical storm Hanna Thu. evening & into the Atlantic season’s first hurricane early Saturday (avg. first Atlantic hurricane is Aug. 10). Hanna is the fastest ever to the ‘H’ name beating “Harvey” on Aug. 3, 2005. Hanna continued to organize right up to landfall at 6pm EDT Saturday at Padre Island followed by a second landfall on the Texas coast a couple of hours later as a strong Cat. 1 hurricane with sustained winds near 90 mph including an eye 20-25 miles across. Hanna is the 4th named storm for July which is just short of the record of 5 set in 2005. Two named storms over the Atlantic Basin at the same time in July last happened in 2018 (Beryl & Chris). Other times since 2000 (Klotzbach): 2011, 2008 & 2005. Hanna continues to weaken while moving W/SW over far Northern Mexico while still dropping torrential rain.

(2) low pressure over the Central Atlantic became tropical depression #7 Tue. & then tropical storm “Gonzalo” Wed. This is the fastest ever to the 7th named storm over the Atlantic beating “Gert” in 2005 by two days. The avg. date of the 7th named storm is not until Sept. 16th. As expected a combination of dry air, shear & proximity to the S. American coast eventually destroyed the inner core of Gonzalo which is now an open wave & not anticipated to regenerate while moving westward toward Central America. The last NHC advisory was Saturday.

(3) Tropical waves continue rolling off the coast of Africa. One wave - 92L over the Central Atlantic - in particular has potential to develop. Long range forecast models show a long track across the tropical Atlantic through early Aug. “underneath” the broad & strong Bermuda high. Forecast models, of course, have been & continue to be at odds with one another & sometimes at odds with themselves (from one cycle run to the next). It’s way too early to get too caught up in the modeling or to start to panic(!). The European has the system in the Western Caribbean by the weekend/early next weak & has trended much weaker & farther south with recent operational runs showing a move west through the Caribbean (although ensemble members still indicate a potential northward move)... the GFS is faster & has the system east of Fl. by late in the upcoming week/weekend... & the UKMET is between the two on timing but much stronger indicating a hurricane north of Puerto Rico & close to the Bahamas by the weekend. Overall forecast models recently have generally trended north. Movement will ultimately hinge on the positioning & strength of the Bermuda high over the Atlantic & how quickly (or not) the wave develops. Stronger/earlier development would tend to support a more northward track solution. There is a good deal of shear in the vicinity of the wave now - on the order of 25-30+ mph - so any short term organization will likely be slow. But once farther west, shear relaxes. This in itself may lend to a more westward solution before gaining much latitude. One to watch no doubt!

(4) A little upper level disturbance/trough of low pressure that was left behind from Hanna over the weekend is over the Northern Gulf of Mexico. Disorganized clusters of t’storms are occurring with this feature near the Northern Gulf Coast across Louisiana & Mississippi. The low/upper trough will then emerge over the Western Atlantic by the middle of the week where there could be some potential for tropical development as the low rides on out northeast over the Atlantic. Forecast models are indicating virtually nothing at the moment.

E. Atlantic tropical wave/disturbance spaghetti plots:

Meanwhile... “velocity potential anomalies” map below shows why we’ve had more tropical activity over both the E. Pacific & Atlantic. The green lines indicate “upward” vertical velocities which are shown to be in a narrow but strong corridor spreading from the Eastern Pacific into the Atlantic Basin. This upward motion in the atmosphere often correlates with increased t’storm activity & sometimes tropical development & is right in concert with the development of tropical cyclone Douglas over the E. Pacific & Hanna over the W. Gulf last week.