(EUMETSAT)

A tropical disturbance that just left the African coast Sunday has become the hurricane season’s ninth named storm over the eastern tropical Atlantic Ocean. The National Hurricane Center declared that Tropical Storm Irma had formed at 11 a.m. Eastern time, and it is expected to strengthen. It is many days away from any land, but it should be monitored by interests in the Caribbean and United States.

Meanwhile, a tropical system that could form in the western Gulf of Mexico near Louisiana and Texas early next week bears watching.

Irma

Irma’s was positioned 420 miles west of the Cabo Verde Islands on Wednesday, with maximum sustained winds of 50 mph. It was tracking west at 13 miles per hour.


(National Hurricane Center)

Computer models are in excellent agreement that this storm will intensify in the coming days and could reach hurricane intensity by Friday or this weekend. It is still very far east — more than 2,000 miles east of the Leeward Islands — so there is plenty of time keep a watchful eye on it. Through the next four days or so, models also agree on where it will track, but beyond that, some potentially important divergence sets in.


Model track forecasts over the next five days from a selection of global and regional models. (tropicalatlantic.com)

The farther north it goes, the more likely it becomes that it will recurve to the north and away from land. But if it stays farther south, away from weaknesses in a large area of high pressure in the subtropics (to its north), it can keep cruising toward the Caribbean, Central America, Mexico and possibly the United States.

Waves were seen lapping over Interstate-10 near Winnie, Tex., on Aug. 29 as floodwater continued to rise. (Logan Wheat)

Gulf of Mexico system

Another area we continue to monitor is the northwestern Gulf of Mexico. Just days after Harvey moves out, another tropical disturbance or tropical cyclone could move in. It does not yet exist, but models have consistently been hinting at a disturbance developing in the Bay of Campeche and tracking toward Texas by Wednesday.

The latest run of the U.S. GFS model produces 10 to 15 inches of rain in a swath spanning Southeast Texas through southern Louisiana. There is still a lot of uncertainty with this system, but given the potential, it is important to be aware of it. If it develops but tracks a bit further east, the Texas coast could be spared.


Accumulated rainfall forecast from Wednesday morning through next Thursday. About two to six inches of these totals is still from Harvey along the Texas-Louisiana border between Lake Charles and Shreveport, La. (tropicaltidbits.com)

Hurricane season status update

Historically, over the past 50 years, the ninth named storm has formed Sep. 30, on average, so Irma is exactly one month ahead of par. Accumulated cyclone energy, or ACE, is another useful metric we commonly use to assess how busy the hurricane season is. It is a single value that integrates information about all of the various storms’ intensities over their entire life span. The ACE so far this hurricane season is at only about 92 percent of average, despite Harvey.


Average timeline of ACE accrual (blue) with the 2017 season superimposed (yellow). (B. McNoldy)

Harvey’s rampage in the Gulf of Mexico and Southeast Texas aside, the hurricane season is still young and just approaching its peak.