Published: November 6,2015
The
Atlantic hurricane season is not over yet, and two areas are being
monitored for possible tropical cyclone development in the coming days.
Since
Hurricane Joaquin dissipated just about a month ago, the tropics have
been quite quiet in the North Atlantic. A persistent pattern
characterized by record levels of wind shear has been a driving force in
inhibiting tropical development.
Nonetheless,
a window of opportunity is opening for at least one and possibly two
systems to grow into bona fide tropical cyclones.
Tropical Setup
System Near Lesser Antilles the More Likely Threat
The area near and just east of the Bahamas is no stranger to late-season 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 near Puerto Rico on 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 188.8 millimeters
(7.43 inches) of rain since Thursday, as of 8 p.m. AST Friday. 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 to the Dominican Republic and Haiti
through the weekend.
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. No direct
threat to Florida is anticipated, but increased surf would be possible
along Atlantic-facing shores of the Sunshine State if the system
generates strong winds.
Further
north, some shower and thunderstorm activity from the system 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.
Lesser Threat Near the Bay of Campeche
A
flare-up of convection has been observed over the Yucatan Peninsula, in
the presence of warm sea-surface temperatures across the adjacent
western Caribbean and Gulf of Mexico.
The areas across the North Atlantic where tropical cyclones have formed in November in the past.
Many
November tropical systems have formed in this region in the past,
almost always on the Caribbean side of the Yucatan. Although there is
some potential with this particular system, the odds are relatively low.
After
this disturbance passes over the Yucatan, there is a very small window
of opportunity for development over the Bay of Campeche.
While
wind shear appears low in the vicinity in the short-term, an increase
winds aloft due to a southward-sinking cold front should work 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 early
in the coming week.
Either way,
shower and thunderstorm activity associated with the system should
increase across the western Gulf of Mexico, along with an increase in
wave action from the Texas Gulf Coast to the mouth of the Mississippi.
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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