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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 171947

Area Forecast Discussion
National Weather Service Key West FL
247 PM EST Sat Feb 17 2018

An upper-level composite analysis this afternoon reveals an
expansive deep layer mean anticyclone centered over the
subtropical western North Atlantic, with ridging extending
northward and westward for several hundred miles. A mostly dry and
stable atmosphere persists across the Florida Keys, with sunny
skies populated by only a few transient and shallow cumulus and
stratocumulus varieties. Light to gentle east-southeast breezes
are bathing the Florida Keys in above-average warmth and 
humidity. Current air temperatures in most Keys island communities
are near 80F, with dewpoint temperatures in the upper 60s. 

During the next 24 hours, a weak high pressure cell extending from
the western North Atlantic to Gulf of Mexico will coalesce with an
intensifying high pressure area beneath an amplifying long-wave
ridge over eastern North America. As a result, easterly flow will
both deepen and strengthen locally. The easterly flow regime will
persist for much of next week, and sky cover and rain chances will
spike during transits of at least three easterly-flow
perturbations. The first (and smallest) disturbance will migrate
through the service area tomorrow (Sunday) morning. The second
(and largest) disturbance will transit the area Monday night. The
third disturbance likely will reach the Keys Wednesday night or
Thursday. Between disturbances, mostly clear skies and rain-free
conditions will prevail. Air trajectories will persist off
surrounding subtropical ocean areas, maintaining a feed of
maritime tropical or highly modified continental air into the
Keys. As a result, air temperatures will remain several degrees
above average for the next seven days. 

No watches, warnings, or advisories are in effect for Florida Keys
coastal waters. However, Small Craft Advisories may be required by
Sunday night, as easterly breezes freshen. Thereafter, fresh to
strong, mainly easterly or east-southeasterly breezes will persist
across Florida Keys coastal waters through Friday or Saturday.

VFR will prevail at the EYW and MTH terminals through the evening. 
Upstream satellite derived TPW products, in conjunction with 
forecast soundings, indicate increased low level moisture overnight 
at both terminals. Expect SCT to BKN layers of clouds to develop at 
025 and 060 around 06Z. Introduced VCSH for both terminals after 12Z 
as low level convergence increases along a moisture undulation. 

Key West  72  81  72  80 / 10 20 10 10 
Marathon  72  82  72  81 / 10 20 10 10 



Data Collection......Chesser

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