Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 260126 AAA
Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
926 PM AST MON JUL 25 2016
.UPDATE...Showers have been slow to diminish over southwestern
Puerto Rico but tops are much lower now and generally under 22
kft. Showers are increasing around the U.S. Virgin Islands and
have increased the POPs there and in eastern Puerto Rico by one
category in select areas. The precipitable water from the 26/00z
sounding came in at almost the same value as the 25/12z sounding
but lower than 24 hours ago. It is expected to increase
considerably overnight and into Tuesday morning with a concurrent
increase in shower activity. Showers will continue to be active
through the afternoon--especially in western Puerto Rico.
.DISCUSSION...The tropical wave can be seen to be rapidly
advancing toward the area and should arrive in the early morning
hours. The current forecast represents little change in timing or
intensity, but confidence is higher in shower activity. Although
thunderstorms cannot be completely ruled out, thunderstorms are
not expected until Tuesday late morning or early afternoon.
.AVIATION...Mostly VFR conditions with passing -SHRA across the
Leeward, USVI and E PR flying area as a tropical wave passes by
tonight thru Tues. HIR terrain will be obscured. SHRA/TSRA
expected over W PR with areas of mtn obscurations between 16Z-22Z,
resulting in brief periods of MVFR conds at TJBQ/TJMZ. Low level
winds prevail E at 5-10 kts, increasing to 10-20 kts with sea
breeze variations after 14Z.
.MARINE...Marine conditions remain more or less tranquil though
winds and seas will gradually increase through Tuesday. Although
small craft advisories are not expected during the next 7 to 10
days, small craft may need to exercise caution in the Atlantic
waters later tomorrow.
.PREV DISCUSSION... /issued 205 PM AST MON JUL 25 2016/
SYNOPSIS...Tropical wave will move across the area Tuesday. SAL
will encompass the region Wednesday and Thursday. Next tropical
wave is expected on Sunday.
DISCUSSION...Mostly sunny skies prevailed across Puerto Rico and
the U.S. Virgin Islands this morning. Some light passing showers
affected the local islands..but were brief. This afternoon...some
showers with thunderstorms developed over the western interior and
northwest sections of Puerto Rico. This activity was locally
induced and should dissipated near sunset.
For tomorrow...a Tropical wave is expected to affect the local
area...increasing the changes for shower and thunderstorm activity
across the region. After the passage of this wave...an area of
Saharan air layer is expected to move across the region...which
will suppress the shower development across the region. It is not
until Sunday...better chances for showers and thunderstorms are
expected as an active tropical wave moves across the region.
AVIATION...VFR conditions expected during most of the period.
-SHRA expected across the Leeward, USVI and E PR flying area from
time to time during the afternoon. Brief periods of MVFR are
likely across western PR, due to SHRA/TSRA between 25/19Z-22z.
E-ESE surface winds at 15 to 20 kt with sea breeze variations and
higher gusts in/near shra/tsra. Winds are expected to drop at 5 to
15 knots overnight, although higher gusts can be expected in SHRA.
MARINE...Seas up to 5 feet and winds up to 20 knots are expected.
Small Craft should exercise caution mainly across the atlantic
PREV DISCUSSION... /issued 1122 AM AST MON JUL 25 2016/
No changes were made to the previous forecast. Cloudiness
increased across the interior and western sections of Puerto
Rico, as well as downwind from The US Virgin Islands late this
morning. Therefore, periods of moderate to heavy showers across
the western half of Puerto Rico are likely this afternoon. In
addition, afternoon shower activity can be expected across the
eastern half from time to time. Satellite images and model
guidance suggested the arrival of a tropical wave by Tuesday, it
will increase the chance of moderate to heavy showers and
thunderstorms across the CWA.
VFR conditions expected during most of the period. -SHRA expected
across the Leeward, USVI and E PR flying area from time to time
during the afternoon. Brief periods of MVFR are likely across
western PR, due to SHRA/TSRA between 25/16Z-22z. E-ESE surface
winds at 15 to 20 kt with sea breeze variations and higher gusts
in/near shra/tsra. Winds are expected to drop at 5 to 15 knots
overnight, although higher gusts can be expected in SHRA.
The local buoy network reported seas between 2 and 5 feet with
winds around 10-15 knots. However, small craft operators should
exercise caution due to winds up to 20 knots across the coastal
waters of Northern Puerto Rico during the afternoon hours. The
potential for showers and thunderstorm are expected to increase
tomorrow as a tropical wave moves across the local waters.
PREV DISCUSSION... /issued 526 AM AST MON JUL 25 2016/
SYNOPSIS...Mid level ridge over the western Atlantic will shift
westward over the next few days. Deep moisture associated with a
tropical wave is forecast to reach the local region on Tuesday.
Upper level trough/TUTT will dig southwestward and relocate over
the region between Thursday and Friday. Another tropical wave
expected late in the weekend.
DISCUSSION...Satellite loops indicated bands of moisture embedded
in the trade wind flow approaching the Northeast Caribbean Region.
This moisture advection over the local area have resulted in showers
affecting the regional waters and the windward areas. Additional
showers will move inland over portions of the U.S. Virgin Islands
and eastern Puerto Rico the rest of the morning. Stronger showers
and isolated thunderstorms are expected to develop over portions
of the West Interior and parts of the Northwest Puerto Rico this
afternoon. The U.S. Virgin Islands will experience isolated to
scattered showers at times.
Operational models indicate deep moisture associated with a tropical
wave reaching the local region on Tuesday. This will result in another
round of showers and thunderstorms across the local area. Moisture
and instability will diminish on Wednesday...reducing the shower
coverage across forecast area.
Unstable conditions will likely return to the islands at the end
of the work week as a upper trough/TUTT will move over the islands.
Then...another tropical wave is forecast to reach the local region
during the weekend. Therefore...moist and unstable pattern will
be likely the second part of the week.
AVIATION...Mostly VFR conditions are expected to prevail with
passing -SHRA across the Leeward, USVI and E PR flying area.
SHRA/TSRA expected over western PR with areas of mtn obscurations
between 16Z-22z, resulting in brief periods of MVFR conds at
TJBQ/TJMZ. Low level winds prevail E-ESE at 10-20 knots with sea
breeze variations after 14Z.
MARINE...Mariners can expect seas of 3-5 feet and winds around
10-20 knots over the next several days. Small craft operators should
exercise due to winds up to 20 knots across the coastal waters of
Northern Puerto Rico. Winds and seas may increase significantly
during the weekend as a stronger tropical wave moves across the
.PRELIMINARY POINT TEMPS/POPS...
SJU 77 89 81 90 / 60 60 30 30
STT 80 87 81 88 / 60 60 30 30