Area Forecast Discussion
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FXUS62 KKEY 200140

Area Forecast Discussion
National Weather Service Key West FL
940 PM EDT Tue Mar 19 2019

After a lull in the precip activity across the Keys during the
late afternoon hours, stratiform rain coverage and embedded shower
coverage has increased once again during the mid evening, although
most of the rainfall remains light at this time. Skies are cloudy
over the Keys, with temperatures mostly in the lower 70s, and
winds on land from the northeast at 15 to 20 mph. Surface analysis
indicates that a weak low pressure area is likely located near the
northwest coast of Cuba, while water vapor satellite imagery shows
one more disturbance moving eastward across the southeastern Gulf,
with a much drier airmass filling into the central Gulf behind
this feature. The 00Z Key West sounding remained very moist with
PW of 1.74 inches, which is well above the 90th percentile for
this date.

In the short term, expect mostly stratiform light to moderate
rain to continue across the Keys for the rest of the evening. An
isolated embedded heavier shower or even a thunderstorm cannot be
ruled out over the island chain, but it is more likely that any
thunderstorms will remain over the Straits and south of the Keys.
As the disturbance currently in the SE Gulf moves quickly eastward
across the Keys late tonight, shower activity should taper off
over the Keys and Gulf waters as the primary area of deep moisture
and lift shifts SE into the eastern Straits. Otherwise, windy
conditions should also taper off late tonight, and low temps
should drop only a few degrees into the upper 60s. The public
forecasts have been updated to reflect the above thinking.

A much drier pattern remains on track for the Keys beginning
Wednesday, with rain chances tapering off to slight, then none by
Thursday afternoon. Expect mostly clear, dry and seasonable
weather for Thursday through Saturday, with highs in the upper 70s
to near 80 and lows in the mid 60s to near 70. Scattered showers
may return to the area beginning Sunday and continuing into early
next week, but recent model guidance has trended drier, and later
shifts may reduce rain chances for those periods.


NE winds have gradually decreased across much of the Keys coastal
waters during the evening, but recently surged back up to 27 knots
sustained at Pulaski Shoal Light. This may be due to the low
pressure area passing to the south of the western Straits at this
time. Winds are currently running below 20 knots at most of the
other reporting sites, but short-range model guidance suggests
that winds will surge back up above 20 knots across much of the
marine area during the next several hours as the low passes to our
south. Will maintain the Small Craft Advisory for all zones with
the late evening forecast issuance. We do expect winds to begin
decreasing toward morning, and to continue dropping on Wednesday.


Large area of light to moderate stratiform rain will spread
across the terminals for the rest of this evening. Heaviest rain
with lowest cigs/vsbys will come later this evening in the 02z-
05z time frame. During that time, cigs below 010 and vsbys in the
4- 6SM range are possible, as indicated in GFS statistical
guidance. Heavier rain should then taper off to showers before
midnight. The boundary layer will remain richly moist into Wed
morning, with GFS LAMP guidance carrying MVFR cigs in the 010-020
range until 17z at EYW. Have only shaved this expectation a little
with scattering indicated at 16z (noon) in the TAFs. The HRRR
even shows cigs hovering just below 010 on a temporary basis as
late as 14z-15z on Wed morning. Expect rapid scattering and
lifting of cloud bases after about 16z to 17z.


On this date in Florida Keys weather history, in 2003, the low
temperatures at Key West (78F) and Marathon (79F) were both warmer
than the high temperatures recorded today. The high at Key West
today was 75F and at Marathon it was 77F.

The low at Marathon on March 19th, 2003 was the first of 3 days
in a row with a low temperature of 79F, tying as the warmest low
temperature ever recorded in the month of March.


GM...Small Craft Advisory for GMZ031>035-042>044-052>055-072>075.



Data Collection......DR

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