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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 151739

Area Forecast Discussion
National Weather Service Key West FL
139 PM EDT Wed Aug 15 2018

An outflow boundary is currently pushing through the Lower Keys.
Boca Chica may see wind gusts approaching 40 knots. The boundary
was initiated by convection just north of the Cuban coast this
morning, and has traversed the breadth of the straits through the
day. Some convection has initiated in the wake of the boundary,
but outside of this activity Key West radar is finding few
returns. An ASCAT pass at 15Z found winds in the Florida Straits 
between 15 and 20 knots. The marine platforms along the reef, 
outside of the convection, are generally near 15 knots. Island 
stations have been near 10 knots.

Overnight and Thursday...The convective events through this
morning and early afternoon confirm the veracity of the guidance
in the placement and extent of the northern portion of the 
wave moving though the Caribbean. However, north of the Lower 
Keys seems to still be entrenched in the drier air and could very 
well be escape and convective cells. With respect to the guidance,
will not separate the Keys in the zone forecast package and keep 
mid- chance pops through tonight. In the overnight hours, and by 
tomorrow morning (Thursday), the wave will have moved off to the 
west and dry air push in behind it. PW values should drop off near
1.5 inches by late tomorrow morning, with relative humidity in 
the convective layer (700-500mb) dropping below 30 percent. This 
will effectively suppress any convection by mid morning.


Model guidance consensus has been fairly consistent in keeping 
the SAL overhead through early Saturday morning which will limit
convective development through this period. Both available GSMs 
show another perturbation in the easterly flow coming through on 
Saturday morning-afternoon, with PW jumping up once again to near
2 inches. After this moves though on Saturday, drier stable air 
once again becomes the dominant feature though Wednesday next 
week. Given the uncertainty in the timing of individual features, 
will hold at low chance pops from Saturday onward at this time. 


Moderate to fresh east to southeast breezes can be expected to
persist over the waters of the Florida Straits this evening and
overnight. With these winds, small craft should exercise caution 
over in the Straits this evening and overnight. Moderate east to 
southeast breezes can be expected elsewhere this evening and 
overnight. Showers and isolated thunderstorms are possible, 
especially in the waters around the lower Keys, the Straits 
waters south of the Lower Keys, and Gulf waters west and north of
the Lower Keys. 


Although VFR conditions will prevail at both the Key West and
Marathon terminals this evening and overnight, passing showers
could bring brief periods of MVFR conditions. This is more likely
to occur at the Key West terminal than the Marathon terminal. 
Near surface winds will be out of the east southeast near 10 


Key West  82  90  82  90 / 40 20 20 20 
Marathon  83  91  82  91 / 40 20 20 20 




Data Collection......BT

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