Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 180103
Area Forecast Discussion
National Weather Service San Juan PR
903 PM AST Tue Jan 17 2017
.UPDATE...An area of moisture across the Atlantic waters will
continue to move southwestward tonight. Under an east northeast
low level wind flow some of these showers will move across the
eastern and northern sections of Puerto Rico as well as across the
USVI, Vieques and Culebra this evening and overnight. However, due
to the rapid movement of the showers the total rainfall amounts
associated with this activity are expected to be minimal.
No major changes are expected in the overall synoptic weather
pattern tonight and Wednesday. A surface high pressure centered
across the southwestern Atlantic and a surface low across the
central Atlantic will continue to induce a moderate east northeast
wind flow across the local islands and surrounding waters with
few passing showers affecting mostly the northern and eastern
sections of Puerto Rico.
GFS model guidance suggests that a surface low will move across
the western Atlantic by Thursday. As this happens, the surface
high pressure is expected to move eastward and weakening, relaxing
the pressure gradient across the local islands. Winds speed are
expected to diminish considerable becoming more from the east late
in the week and during the upcoming weekend.
.AVIATION...Will expect mostly VFR conds over most TAF sites
overnight. However...a band of showers just n of the area will
result in MVFR conditions over TJSJ...TJBQ...TIST...TNCM and
TKPK for short period of time. Low level wnds will remain fm NE-E
10- 15 kts with higher gusts over TIST/TISX.
.MARINE...Winds and seas are expected to diminish overnight. San
Juan buoy 41053 is reporting seas of 4-6 feet and slowly
diminishing. The small craft advisory continues in effect for the
offshore waters and the local passages until early Wednesday
morning. High risk of rip currents are in effect until Wednesday
.PREV DISCUSSION... /issued 151 PM AST Tue Jan 17 2017/
SYNOPSIS...Surface high pressure will remain causing a moderate
to fresh east-northeasterly wind flow until Wednesday before a
surface low enters the western Atlantic Late Wednesday and
weakens the surface High pressure, disrupting the current pattern
and causing the local winds to diminish significantly. Relatively
dry air moves in and an upper trough across the east to northeast
of the local islands will maintain a mostly fair weather pattern
with limited rainfall for the next several days, than a broad
upper level bridge dominates the area towards the end of the
DISCUSSION...Some showers were observed in the early morning
hours, some of them moderate over NE PR, but after mid morning
very few showers were observed while the conditions improved over
land even though some showers persisted over the local waters
under an east northeast wind flow. Since relatively dry air is
moving in, only isolated to locally scattered showers are expected
this afternoon across northern, western and SW-PR. For tonight
and Wednesday the pattern is expected to continue like it has
been for the past few days with isolated to scattered showers in
the overnight hours and early morning while little shower activity
in the afternoon.
For Thursday and the latter part of the workweek, it is still
likely that a surface low moves into the western Atlantic. This
low will weaken the SFC high and the local winds will diminish
significantly. The local temperatures are expected to remain near
normal but with the lighter winds on Thursday there may be cooler
temps during the night on the latter part of the week.
AVIATION...VFR conds will prevail entire prd. Few CU/SC clds lyrs
nr FL025...FL050...CLR abv. Low level wnds fm NE 15-20 kts blo
FL200...BCMG fm W abv and incr w/ht to max wnd btw 70-80 kts nr
FL400. Passing -SHRA/SHRA en route mainly ovr offshore Atl waters N
of islands. SFC wnd fm NE 10-15 kts w/ocnl gusts of 20-25 kts psbl
bcmg fm E 5-15kt aft 17/23z. No sig operational impacts attm.
MARINE...Local nearshore buoys are reporting seas of 4-6 feet
which is consistent with the local forecast. For that reason the
small craft advisory continues in effect for the offshore waters
until late tonight. High risk of rip currents also are in effect
until late tonight. Winds and seas are expected to significantly
improve starting late Wednesday.
.PRELIMINARY POINT TEMPS/POPS...
SJU 73 81 71 81 / 30 30 10 10
STT 72 82 70 82 / 30 20 20 20
PR...High Rip Current Risk through Wednesday afternoon for Culebra-
Mayaguez and Vicinity-North Central-Northeast-Northwest-San
Juan and Vicinity-Southeast-Western Interior.
Small Craft Advisory until 6 AM AST Wednesday for Northeast.
AM...Small Craft Advisory until 6 AM AST Wednesday for Anegada
Passage Southward to 17N-Atlantic Waters of Puerto Rico and
USVI from 10 NM to 19.5N-Mona Passage Southward to 17N.