Sunrise 5:20 AM   Sunset 5:54 PM Moonrise 1:25 AM   Moonset 1:52 PM

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FXCA62 TJSJ 020905 AFDSJU

Area Forecast Discussion National Weather Service San Juan PR 505 AM AST Thu May 2 2024

SYNOPSIS

Unstable conditions and increasing moisture levels will likely persist during the rest of the workweek into the upcoming weekend, as a mid to upper level trough lingers over the western Atlantic and moisture from the Caribbean is steered by east to southeast winds into the area. There is an elevated threat for flooding across all the islands, particularly on Friday and Saturday. The precipitable water content is forecast to remain at normal to above normal levels through the long term period.



SHORT TERM
Today through Saturday...

Overnight, mostly calm weather conditions prevailed over land, with a few showers developing along the eastern half of Puerto Rico and the U.S. Virgin Islands. Nonetheless, showers and thunderstorms were the dominant weather feature over the offshore Atlantic waters through the night. The rainfall accumulations across the islands were around half an inch. Minimum temperatures were in the low to mid-70s across coastal areas and the mid-60s across the higher terrains.

The inherited forecast remains unchanged as wet and unstable conditions continue to evolve. This pattern, driven by an upper- level trough approaching the area from the west, an induced surface trough developing north of the region, and the introduction of additional moisture from the Caribbean, will continue to enhance shower and thunderstorm development across the local area. Later today, expect more moisture to filter across the islands. At this time, the forecast leans toward Friday into Saturday being the most active days, with showers and thunderstorms being the dominating features, particularly along the eastern half of Puerto Rico and the U.S. Virgin Islands. By the end of the workweek, an upper-level maxima will move across the islands with winds around 80 knots.  On Saturday, the yet maxima should remain to the north of the area.
Nonetheless, winds around 70 knots will still reach the region.
The Precipitable Water (PWAT) model guidance shows values above normal climatological levels by the early part of the weekend. The 500 mb temperatures also suggest values around -8 degrees Celsius on Saturday, meaning that there is an increase in the potential for some isolated thunderstorm activity across Puerto Rico and the U.S. Virgin Islands. As saturated soils prevail, any brief period of heavy showers or persistent light rainfall could lead to urban and small-stream flooding,  localized flash flooding and mudslides, particularly across the  the interior, the eastern half of Puerto Rico, and the U.S. Virgin Islands. We encourage citizens and visitors to be aware of any additional updates in the forecast.

Temperature-wise, they will stay in the upper 80s to low 90s along the coastal/urban areas and in the upper 70s to low 80s along the higher terrains.

LONG TERM
Sunday through Thursday...

Lingering moisture and the departing upper level-trough will continue to promote shower and thunderstorm development on Sunday. At lower-levels, a surface high pressure is expected to build over the western Atlantic during the first part of the week. This will promote moderate winds from the east to northeast through the long term period. In addition, the remnants of the previous surface trough to our north or just across the northeastern Caribbean are expected to merge with a frontal boundary across the central Atlantic and linger over the local area through at least Thursday.
Also, at upper levels, another trough will pass mainly to our north from Tuesday onwards, maintaining unstable conditions in general across the region. The highest precipitable water (PWAT)
values are expected during this period, with global guidance suggesting between 2.10-2.25 inches of PWAT from Monday morning through Thursday afternoon. Therefore, any period of moderate to heavy showers across the islands would lead to quick urban and river flooding, as well as mudslides in areas of steep terrain.
Residents and visitors are encourage to monitor the evolution of the weather conditions during the next 5 to 7 days, and stay alert for the issuance of any possible flood watch/warning products.



AVIATION

(06z) TAFS

SHRA/TSRA were observed across the offshore Atlantic waters overnight but dissipated around 02/07Z. VCTS could develop later this afternoon near TJBQ/TJSJ/TIST/TISX, causing tempo MVFR to brief IFR conds. ESE winds at 06-16 kt with stronger gusts near showers.



MARINE

Light to moderate trades and a subsiding northerly swell will promote seas up to 6 feet across the Atlantic waters, and portions of the local passages today. Therefore, small craft operators should exercise caution across these waters. Also, thunderstorm development is likely across the Atlantic waters and the Mona Passage. Lighter winds from the east to southeast and increasing shower and thunderstorm activity is expected during the next several days.



BEACH FORECAST

A subsiding long period northerly swell will continue to promote a high risk of rip currents along the north-facing beaches of Puerto Rico, including Culebra today. A High Rip Current Risk (CFWSJU)
is in effect through late this afternoon.



HYDROLOGY

An upper-level trough and an induced surface trough should promote wet and unstable conditions throughout the weekend, particularly on Friday and Saturday. There is an elevated flood threat due to saturated soils across portions of the islands. Please refer to the latest Hydrologic Outlook (ESFSJU) for more information.



SJU WATCHES/WARNINGS/ADVISORIES
PR...High Rip Current Risk through this afternoon for PRZ001-002-005- 008-012.

VI...None.
AM...None.

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