703 FXCA62 TJSJ 030916 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 516 AM AST Thu Apr 3 2025 .SYNOPSIS... Lower rain chances are anticipated today due to the arrival of a drier airmass. Today, the main hazard will be the windy conditions, with sustained winds of 20 to 30 mph and gusts potentially exceeding 40 mph, possibly reaching up to 50 mph in localized areas. These wind conditions are expected to continue into Friday. These conditions will also elevate the risk of fires, especially in grass-dominated areas. As a result, a Fire Danger Statement (RFD) has been issued for today. && .SHORT TERM...Today through Saturday... Showery weather persisted overnight, as gusty winds helped trigger shower development, particularly across windward coastal areas. Gusty wind conditions were also reported by weather stations, especially due to passing showers. Maximum wind gusts of 25 to 30 mph were observed across the windward coastal regions of Puerto Rico and the surrounding smaller islands. A similar weather pattern is expected to continue through the morning hours. However, a sudden decrease in shower activity is anticipated by this afternoon, as a dry slot, detected by GOES-16 satellite data, moves over the area. PWAT values are forecast to drop below 1.0 inch across the region. Winds will increase throughout the day, with sustained winds of 20 to 30 mph and gusts potentially exceeding 40 mph, possibly reaching up to 50 mph in localized areas. These wind conditions are expected to continue into Friday, though slightly weaker than today. As a result, a Wind Advisory remains in effect through 8 PM AST Friday. These conditions could lead to difficult driving, especially for high-profile vehicles on bridges or exposed roadways. Tree limbs or weak trees may break and fall onto power lines, and outdoor items could be blown around or damaged. Minor damage to poorly secured structures is also possible. Winds will gradually subside through the weekend, though breezy conditions will persist as the pressure gradient over the northern Caribbean continues to loosen. In terms of shower activity, a mid-to-upper-level trough is expected to deepen through the short-term forecast period. Several indicators of favorable dynamics will be present, including 250 mb height falls, reduced 1000-500 mb thicknesses, cooler 500 mb temperatures, and steeper 700-500 mb lapse rates. However, moisture availability will remain the limiting factor, with precipitable water values falling to below-normal levels today and Friday, and 700-500 mb relative humidity dropping nearly two standard deviations below normal. During these drier periods, passing showers may develop during the night and early morning hours, with scattered showers forming in the afternoon over interior and western Puerto Rico. The greatest potential for any thunderstorm activity is expected on Saturday afternoon, coinciding with a brief increase in moisture levels to near-normal values. .LONG TERM...Sunday through Thursday... Starting the long-term period, winds will continue to subside, allowing hazardous marine and coastal conditions to improve, at least through next Monday. Latest model guidance continues to suggest that a surface high-pressure over the western Atlantic will move eastward into the Central Atlantic from Sunday into early next week, promoting east to northeast winds to become more easterly from Monday onward. An upper-level trough will persist over the region through the forecast period, promoting ventilation and cooler temperatures aloft, with 500 mb temperatures remaining between -8C and -10C. These conditions will support favorable conditions for deep convection and increase the chances of thunderstorm development. However, moisture content will be limited across different levels of the atmosphere, which could inhibit significant rainfall and afternoon thunderstorms. Models suggest that precipitable water values will oscillate between below 1.0 and 1.5 inches through Tuesday, which is considered below normal to near average. As a result, activity will likely depend on the arrival of patches of moisture, leading to periods of sunshine and passing showers each day. Local effects and favorable conditions aloft will likely produce isolated to scattered convection, with a thunderstorm or two, during the afternoon hours across the western portions of Puerto Rico each day. However, at the moment, significant accumulations are not expected. By Wednesday, the arrival of a band of moisture will produce better rain chances. From Thursday afternoon/night onward, it seems that we will transition into a wetter pattern due to the combination of an approaching surface frontal boundary, a pre- frontal trough, and the arrival of abundant tropical moisture under southeasterly wind flow across the islands. This will likely increase the frequency and chance of showers by the end of next week. && .AVIATION... (06Z TAFs) Mostly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, passing SHRA will move in the vicinity of TJSJ/TJBQ/TIST/TISX through 03/15z. E/ENE winds of 20- 25 kt will persist today, with gusts between 30 and 40 knots, but could be higher, blo FL050. Therefore, a Wind Advisory is in effect for the islands. && .MARINE... A broad surface high pressure over the western Atlantic will continue to promote fresh to locally strong east to east-northeast winds through at least late Friday night, then conditions will gradually improve Saturday into Sunday. Today, seas will continue to build between 6 to 10 feet, and occasionally higher, across most waters resulting in hazardous seas over the next few days. && .BEACH FORECAST... A broad surface high pressure over the western Atlantic is producing strong winds across our area, especially in coastal areas today through late Friday. This will maintain coastal conditions deteriorated through at least Saturday. For that reason, a High Rip Current Risk remains in effect through Saturday afternoon for the north-facing beaches of Puerto Rico, from Aguadilla to Fajardo, Culebra and the U.S. Virgin Islands. Also, from today through at least Friday evening there will be a High Rip Current Risk for the beaches of southeastern Puerto Rico, from Salinas to Yabucoa, and Vieques. A Moderate Risk is in place elsewhere. Swimmers are urged to exercise caution by staying near lifeguards or even better to stay out of the water. Rip Currents can sweep even the best swimmers away from shore into deeper water, where it becomes difficult to return to safety. Heed the advice of lifeguards, beach patrol flags and signs. && .FIRE WEATHER... Although most of the island has received above-normal rainfall over the past month, smaller, fire-prone coastal regions continue to observe below-normal precipitation. A dry slot will lead to relative humidity values dropping to 40 to 45% across the southern coastal plains, and possibly 50 to 55% across northwestern Puerto Rico, an area with the lowest 30-day and 60-day percent of normal rainfall. Combined with this dry air, windy conditions are expected today, with easterly winds likely reaching up to 25 mph or higher, and gusts potentially exceeding 30 mph. The KBDI was reported at 349 in Cabo Rojo and 628 in Guanica, indicating that areas with dry vegetation and available fuels could experience rapid fire spread today. These conditions elevate the risk of fast-moving fires, especially in grass-dominated areas. As a result, a Fire Danger Statement (RFD) has been issued for the affected regions. Please refer to RFDSJU for further details. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Saturday afternoon for PRZ001-002- 005-008-012. Wind Advisory until 8 PM AST Friday for PRZ001>013. High Rip Current Risk through Friday evening for PRZ003-013. VI...High Rip Current Risk through Saturday afternoon for VIZ001-002. Wind Advisory until 8 PM AST Friday for VIZ001-002. AM...Small Craft Advisory until noon AST Saturday for AMZ711-712-716- 723-726-733-741. Small Craft Advisory until 6 AM AST Friday for AMZ735-742-745. && $$ SHORT TERM/AVIATION/FIRE WEATHER...CVB LONG TERM/MARINE/BEACH FORECAST...YZR
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