Published: November 7,2015
The
Atlantic hurricane season is not over yet, and one area continues to be
monitored for possible tropical cyclone development in the coming days.
Since
Hurricane Joaquin dissipated just about a month ago, the tropics have
been quiet in the North Atlantic. A persistent pattern characterized by
record levels of wind shear has been a driving force in inhibiting
tropical development this season.
Nonetheless,
a window of opportunity is opening for at least one system to grow into
a bona fide tropical cyclone in the days ahead.
Tropical Setup
System Near Lesser Antilles the More Likely Threat
The area near and just east of the Bahamas is no stranger to November tropical formation.
The typical areas of tropical cyclone development across the North Atlantic, including the common tracks of such systems.
With
a plume of rich, tropical moisture feeding north from the Caribbean and
wind shear forecast to relax north of the Greater Antilles, a tropical
wave moving toward that area from the Lesser Antilles poses a threat to
become better organized by early in the coming week.
Wind
shear is not kind to tropical systems. The change in wind speed and
direction with height works to tear apart the structure of a tropical
system, either causing one to dissipate, or limiting the ability of such
a system to better organize.
Computer forecast
models show this wave developing into a better-defined area of low
pressure north of Hispañola Sunday. As the system moves into the open,
warm waters east of the Bahamas, organization into a tropical depression
or tropical storm is at least possible.
The
tropical wave has already doused parts of the Lesser Antilles with
excessive rainfall. Martinique had already picked up 192.4 millimeters
(7.57 inches) of rain since Thursday, as of 8 p.m. AST Saturday. Most of
that fell Friday, causing serious flooding on parts of the island.
As
the system moves northwest, heavy rain, flash flooding and gusty winds
may be concerns from Puerto Rico and the Virgin Islands to the Dominican
Republic, Haiti, Turks and Caicos and southeast Bahamas through Sunday.
Latest Satellite
(Forecast: San Juan)
Due to atmospheric steering currents on the western periphery of high pressure over the open Atlantic,
the system – tropical or not – would likely be pulled north, then
northeast early in the week ahead, remaining off the Southeast coast. No
direct threat to Florida is anticipated, but some increased surf would
be possible along Atlantic-facing shores of the Sunshine State if the
system can develop appreciably.
Further
north, some shower and thunderstorm activity, with locally heavy rain
could impact the coastal Carolinas next week. This largely depends on
how the potentially-tropical system interacts with another weak area of
low pressure that may develop on the tail end of a lingering frontal
boundary across the Southeast.
This
front is responsible for the recent rain across the southern Plains and
Gulf Coast states and will eventually bring relief to some of the
Florida heat over the next few days.
(MORE: Record Heat Across Florida)
All
things considered, there is a window of opportunity for the tropical
wave to become better organized near the Bahamas and Gulf Stream. In
this area, sea-surface temperatures do remain above average for this
time of the year, providing just enough heat content to support a
tropical cyclone.
As the
system moves further north, increasing wind shear will create a less
favorable environment and the system would then curl northeastward out
to sea, perhaps brushing Bermuda by mid-week.
Development Near the Bay of Campeche Unlikely
A
broad area of low pressure is spinning over the western Gulf of Mexico.
Convection has been flaring up north of the center of circulation, but
not near its center, so far.
The areas across the North Atlantic where tropical cyclones have formed in November in the past.
Very
few November tropical systems have formed in the Gulf of Mexico.
Instead, they almost always form in the western Caribbean Sea east of
Mexico's Yucatan peninsula, or elsewhere in the western or central
Atlantic Ocean. Although there was some potential with this particular
system, further development now appears unlikely.
Wind
shear was initially low in the vicinity of the disturbance, but an
increase winds aloft due to a southward-sinking cold front is working
against any substantial organization.
Furthermore,
while some computer models do show the system spinning up a modest area
of low pressure over the next day or so, the approaching cold front
will likely overcome the system. The result would be degradation of the
tropical wave early in the coming week.
Either
way, shower and thunderstorm activity associated with the system should
increase across the Gulf Coast the next couple of days, with a threat
of local flash flooding from Texas to northern Florida.
November Climatology in the Tropics
The
Atlantic hurricane season officially comes to an end on Nov. 30. With
the ocean cooling from north to south, particularly at the
mid-latitudes, the formation zone for tropical systems shrinks.
The number of tropical storm and hurricane impacts by state in the month of November.
Although
the Gulf of Mexico stays relatively warm through much of the month,
historically, as the jet stream shifts south, the environment tends to
become increasingly hostile due to stronger wind shear.
In
the period of record from 1851 to 2014, no tropical storm or hurricane
has impacted the western Gulf Coast from Texas to Mississippi.
To
the southeast, systems that do develop across the Caribbean can gain
some organization, as the area has supported such late-season hurricanes
as Kate in 1985 and Michelle in 2001. The former became the latest
landfalling hurricane in Florida’s history on Nov. 21.
(MORE: No Hurricanes Have Struck Florida in 10 Years)
Otherwise,
due to increasing upper level flow, any system that does develop tends
to quickly turn north and northeast into the open Atlantic and away from
the United States.
Since 1851,
Florida has been impacted by eight tropical storms and hurricanes in
November. The only other states with more than one impact were also in
the Southeast: Alabama, Georgia and North Carolina.
MORE: Hurricane Strikes by County, Parish
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