Tropical Depression Four expected to dissipate, but active season looks likely

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Tropical Depression Four is forecast to dissipate before reaching the Bahamas. (Credit: NHC)

Tropical Depression Four looked like it was ready to start intensifying Wednesday night as the National Hurricane Center began issuing advisories on the Central Atlantic system. But it had lost much of its punch on Thursday — a trend NHC forecasters say may signal its ultimate demise.

With one exception, forecast models show the low limping toward the Bahamas by the weekend and then dissipating, falling victim to dry air and higher wind shear.

The National Weather Service in Miami said Thursday: “No impacts expected for South Florida from this tropical depression.” It’s not mentioned at all in Central Florida NWS discussions from Melbourne, where rain chances over the weekend are forecast to tick up slightly thanks to a trough of low pressure over the eastern U.S.

The only forecast model that suggests any future for TD Four is the Canadian (CMC), which has the system reintensifying early next week after it heads north from the Bahamas.

Eastern Atlantic sat

With TD Four (left) churning in the Atlantic, another wave was approaching the coast of Africa Thursday. (Credit: NOAA)

The U.S. East Coast is far from off the hook this month, though, as potent tropical waves continue to roll off the coast of Africa — a phenomenon more typical of August and September. Eventually these waves will encounter lower wind shear and a more moist environment.

The tropical Atlantic is unusually warm — fuel for potential tropical systems — and the heat shows no signs of backing off.

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Sea surface temperature anomalies as of July 3. (Credit: NOAA/ NESDIS)

That’s one of the main reasons why new hurricane season forecasts were bumped up this week by Colorado State University and the United Kingdom’s Tropical Storm Risk.

CSU is predicting 15 named storms, including the three already in the books, while TSR is now forecasting 17 named storms. CSU is calling for eight hurricanes and TSR seven. And since none of the three named storms we’ve had reached hurricane status, those hurricanes would most likely be spread out over the next three months. (The hurricane season officially runs to November 30.)

One of the more disturbing parts of hurricane researcher Philip Klotzbach’s CSU analysis, released Thursday, points to six analog years “with characteristics most similar to what we expect to see in August-October of 2017.”

One of them is 2004, which was an infamous hurricane season in Florida that included Charley, Frances, Jeanne and Ivan, although Ivan officially made landfall in Gulf Shores, Alabama.

The other five analog years identified by CSU are 1953, 1969 (Hurricane Camille), 1979 (Hurricane David), 2006 and 2012. The number of hurricanes ranged from six in 1979 to 12 in 1969.

One caveat for this season is that water temperatures in the north-central Gulf of Mexico have been cooler than average.

Whether or not that will become a mitigating factor in this year’s season remains to be seen.

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Author: jnelander

Freelance writer and editor

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