Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 270858
Area Forecast Discussion
National Weather Service San Juan PR
458 AM AST Thu Apr 27 2017
.SYNOPSIS...Surface high will continue across much of the Atlantic
basin for the next several days. Moderate to fresh trade winds
will persist through the forecast period. Short wave trof moves
during the weekend and TUTT pattern is expected through early next
week. Upper ridge builds from the west across the Caribbean basin
by midweek next week.
.SHORT TERM...Thursday through Saturday...
Mostly clear skies prevailed overnight and early this morning across
the forecast area with limited shower activity observed over land
areas. Temperatures were in the upper 70s to low 80s at the lower
elevations under light and variable winds.
A TUTT is expected to develop north of the area by Friday and hold
through the upcoming weekend with the forecast area remaining east
of its axis. At lower levels, a high pressure across the north
central Atlantic will continue to promote moderate trade winds
through early the upcoming weekend. The local pressure gradient is
then expected to tighten later during the weekend as the surface
high relocates across the central Atlantic and north of the islands.
This will result in moderate to fresh trades late Saturday. Although
the latest guidance continues to suggest decreasing trend in
precipitable water during the next day or so, precipitable water
will remain above the normal range.
As a result, expect a mainly fair weather pattern during the early
morning hours with shower and thunder activity increasing across the
forecast area late in the morning and afternoon hours. These showers
and thunderstorms are expected mainly across the northwest quadrant
of the island as well as portions of the San Juan Metro Area. With
the heaviest showers, urban and small stream flooding is likely.
Friday and Saturday a similar pattern with showers in the morning
across windward areas followed by afternoon showers and
thunderstorms across west Puerto Rico is expected, however intensity
and coverage will increase as the TUTT establishes north of the area.
.LONG TERM...Sunday through Friday...
TUTT pattern to the northeast is expected to provide instability
across the area to aid the development of showers and possible isolated
thunderstorms through at least Tuesday afternoon. As upper ridge
builds from the west and surface high relocates just north of the
islands...the available moisture will be confined below 800 mb
from Wednesday through the end of the forecast period. Trade wind
showers and streamers are expected mainly across the USVI`s,
Culebra and Vieques. Across the interior and western portions of
Puerto Rico, diurnally induced scattered showers are expected.
.AVIATION....VFR conds expected to prevail at all TAF sites
through the morning hours. SHRA/TSRA development expected aft
27/16z to result in brief periods of MVFR conds and mountain
obscurations in and around JBQ/JMZ and possibly JSJ through
27/22z. Easterly winds 10 to 15 knots with sea breeze variations
today, becoming light and variable overnight.
.MARINE...Moderate to locally fresh trade winds will continue for
the next several days as surface high pressure across the central Atlantic
continues to build and tighten the local pressure gradient. Short
period wind driven seas will increase across the offshore waters
and passages during the weekend. Overall, winds should remain
between 15-20 knots and highest seas around 6 feet during the
weekend across these waters. Moderate risk of rip currents
expected across much of the northern and southern beaches of the
.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 75 / 30 30 30 30
STT 86 76 86 74 / 30 30 50 50