National Weather Service San Juan PR
455 AM AST Sun Nov 7 2021
.SYNOPSIS...Weak high pressure in the central Atlantic will drive
moderate easterly trade winds over the area. Moisture will
increase on Monday with some brief heavy rain possible. Then
alternating bubbles of moisture and dry air will bring a mix of
showery and fair weather. Mid-levels will remain dry through the
whole week, limiting the amount of rain expected.
&&
.SHORT TERM...Today through Tuesday...
Mid-upper level ridge will continue to be the main feature
dominating the weather conditions in the northeast Caribbean. As a
result, conditions will remain mostly dry and stable over the next
day or so. The overall moisture will continue to diminish through
Monday morning, returning to normal levels late Monday. Based on
this scenario, fair weather is likely to prevail during the next 24
hours. Then, slightly wetter conditions are forecast late Monday
morning and afternoon as a patchof moisture embedded in the trade
winds reaches the islands, triggering a few rounds of scattered
showers. Although additional showers are anticipated, no
significantrainfallaccumulations areexpected due to
generally stable conditions aloft associated with the mid to
upper-level ridge.Thunderstorms over the next 72 hours are not
likely as the air mass at mid-level is warmer than normal and very
dry. On Tuesday, fair weather conditions will return to the
forecast area. However, a few tradewind showers over the U.S.
Virgin Islands/eastern Puerto Rico and localized convection over
western Puerto Rico can`t be ruledout on Tuesday as moisture
remains just below normal.
.LONG TERM...Wednesday through Sunday...
Low pressure that has formed off the coasts of Florida, Georgia
and South Carolina is expected to begin moving east into the
Atlantic on Monday. The GFS has it due north of the forecast area
at about 32 degrees north latitude on Wednesday night while high
pressure at the surface in the Atlantic continues to be the
driving engine behind the moderate easterly tradewinds that will
have been experienced during the first part of the week. As the
low continues to the east, northerly flow at 700 mb will reach
Puerto Rico by Sunday and the GFS does show a mild drop in
thicknesses over the weekend. The drier air behind it will stall
as it is modified by locally warm ocean surface temperatures.
Mid levels will remain dry through the period as high pressure at
500 mb remains in close proximity around the local area. At levels
lower than 700 mb, the high pressure in the central Atlantic,
though weak, will be able to sustain the east northeast trade wind
flow that will carry bubbles of very good moisture and thin bands
of rather dry air across the area, resulting in showery periods
and fair weather marching across the islands at irregular
intervals. Exact timing this far out will be difficult to
forecast, but the dry mid levels will limit any heavy rains that
might have occurred otherwise.
&&
.AVIATION...VFR conditions will prevail through the forecast period.
Stable wx conditions expected across the local area, therefore no
significantimpacts to operations are anticipated over the next 24
hours. SHRA, if any, will form near TJBQ between 18Z-21Z. As a
result, VCSH was included at TJBQ. E to ESE winds of 10-15 kts will
continue below FL150. Max winds N 20-30 knots btwn FL400-445.
&&
.MARINE...Generally tranquil seas of 4 feet or less will be
interrupted by the intrusion of a northwesterly swell from the low
pressure passing well to our north that will raise seas to as much
as 6 feet Wednesday and possible push to high the risk of rip
currents on the north coasts of the local islands. At this time
small craft advisories are not expected this week.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 75 88 75 / 20 10 50 20
STT 88 77 87 77 / 20 50 50 30
&&