Monday, July 10, 2017

Could Last Week's Tropical Depression Four Come Back to Life in the Atlantic? Hurricane Hunter Mission Scheduled

Jon Erdman
Published: July 10,2017

The remnant of last week's Tropical Depression Four continues to sprout thunderstorms, and a rebirth as a tropical cyclone can't be ruled out as it tracks toward the Bahamas and possibly Florida later this week.
(MORE: Hurricane Central)
Located just over 100 miles north of the Virgin Islands, this ghost of what was once T.D. Four had flared some healthy convection Monday and throughout the weekend.

Current Infrared Satellite Image
This disturbance appears to be in an environment of at least some wind shear, or change in wind direction with height, but in an otherwise sufficiently moist atmosphere with winds spreading apart aloft to support these occasional bursts of thunderstorms.
If thunderstorms were to persist and any low-pressure circulation near the surface is found, the National Hurricane Center (NHC) would then resume advisories on T.D. Four, or if winds are strong enough, Tropical Storm Don.
The NHC has tentatively scheduled a Tuesday afternoon hurricane hunter reconaissance mission into this disturbance to see if it has indeed become a depression or storm.
But, for now, this possibility of redevelopment is low.

Where is It Headed?

Whatever the outcome, the same atmospheric steering wheel as was the case last week exists this week.
The feature, namely, the Bermuda-Azores high, responsible for steering the Atlantic tropical disturbance this week.
The Bermuda-Azores high should keep this disturbance on a general west-northwest track.
This should push the disturbance into the Bahamas starting Wednesday, and may give a boost to the typical showers and thunderstorms over parts of the Florida Peninsula starting Thursday.
(FORECAST: Nassau, Bahamas | Miami)
The disturbance will battle at least some modest wind shear and perhaps some dry air before it gets to the Bahamas, so, again, the odds of it redeveloping into a tropical depression appear low.
Beyond that, the disturbance may enter the eastern Gulf of Mexico by the weekend, and would have to be monitored for any development there. If anything, it could lead to another heavy rain threat in parts of the Deep South, where the ground remains soggy from previous heavy rain.
(MORE: Strange Start to the Hurricane Season)
For now, there's nothing to be alarmed about, but it's worth checking back with us for any updates to this forecast over the next several days.
(MORE: Why Long-Range Model Forecasts For the Tropics Can't Often Be Trusted)

Another Tropical Wave to Watch

Much farther east, another tropical wave in the Atlantic is being monitored.
This one is still more than halfway between the west African coast and the Lesser Antilles, several hundred miles southwest of the Cabo Verde Islands.
(MORE: Why We Watch the Cabo Verde Islands in Hurricane Season)
As was the case with T.D. Four last week, this east Atlantic system faces a pair of nemeses to develop.
First, dry air is still abundant from the Caribbean Sea to west Africa, visible in this satellite loop from UW-CIMSS, showing the yellow-, orange- and red-shaded areas pouring southwestward into the strip of the tropics between Africa and the Lesser Antilles.

Current Water Vapor Satellite Image
Secondly, wind shear increases in the Caribbean Sea. Wind shear is the change in wind speed and/or direction with height that can rip apart a fledgling tropical disturbance by blowing thunderstorms away from developing low pressure.
(MORE: A Typical July in the Atlantic Hurricane Season)
So, assuming the dry air doesn't stifle this tropical wave before getting to the Windward Islands by Friday, increased Caribbean wind shear may do so.
At any rate, there is plenty of time to monitor this disturbance, so check back with us at for the latest.
This is a good time to make sure you have a plan in case a hurricane threatens. The Federal Alliance for Safe Homes has an excellent site that can help you make a hurricane plan.
MORE: Atlantic Basin Retired Hurricanes and Tropical Storm Names

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