213 FXCA62 TJSJ 130854 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 454 AM AST Mon Jan 13 2025 .SYNOPSIS... While current long-period northerly swells are subsiding, additional pulses are expected by tomorrow and will once again deteriorate marine and coastal conditions throughout the second half of the week. On the other hand overall generally fair weather an cooler than normal temperatures are forecast for today. Tomorrow, the remnants of an old frontal boundary to bring light to moderate rains steered by northeasterly winds to the U.S. Virgin Islands, Vieques, Culebra, and northern/eastern Puerto Rico in the morning and early afternoon, tapering off by evening. Remnants of past frontal boundaries are also forecast to move into the local islands late Friday and into Saturday. && .SHORT TERM...Today through Wednesday... Radar and satellite imagery indicated mostly clear skies overnight, with a few patches of low-level clouds moving across the region and fog developing in the higher elevations of the interior after midnight, likely affecting parts of highway PR-52 between Salinas and Cayey. Although the broader wind flow remained from the northeast, winds over land were light to calm and variable, with land breezes dominating in coastal areas. Surface observations showed overnight temperatures ranging from the mid-50s in the higher elevations of the Cordillera Central to the lower 70s in coastal areas and local islands. A mid-level ridge drifting over the northern Caribbean will maintain stable conditions throughout the period. Fair weather conditions are expected today, with light to moderate northeast winds and minimal to no shower activity. PWAT values will remain below normal, under an inch. By Tuesday, the ridge`s influence briefly weakens, coinciding with the remnants of an old frontal boundary to bring light to moderate rains from trade wind showers to the U.S. Virgin Islands, Vieques, Culebra, and northern/eastern Puerto Rico in the morning and early afternoon, tapering off by evening. Rainfall totals will be around a quarter inch, with improving conditions after sunset. Northeast to north-northeast winds will strengthen late Tuesday, becoming breezy. The ridge will stretch back into the northeastern Caribbean by Wednesday, while another surface high will yield increased trade winds and wetter conditions. Trade wind showers will affect windward areas, particularly at nighttime, with rainfall totals ranging from a quarter to half an inch. Breezy to windy conditions will persist throughout the day. Overall, temperatures will generally remain cooler-than-normal, with overnight lows in the 50s in higher elevations and 70s along the coast and daytime highs in the mid-80s. For more details, visit the Experimental Graphical Hazard Weather Outlook at https://www.weather.gov/erh/ghwo?wfo=sju. .LONG TERM...Thursday through Sunday... A surface high moving towards the western Atlantic will help promote northeasterly steering flow to start the long term period. Gradually increasing precipitable water (PWAT) values is forecast, however they will still remain at below normal to low end normal values before Friday, around 1.2 in to 1.3 in, with only slightly more humid patches possible. Persistent mid-level ridging and a trade wind inversion will continue to keep most available moisture below 800 mb through most of the period. Northeasterly winds will also promote a cooler temperatures across the islands, with model- estimated 925 mb temperatures at below normal to normal values. Maximum temperatures can reach the low to mid 80s (locally higher) across lower elevation areas of the islands. Minimum temperatures can reach the mid 50s to mid 60s across higher elevations of Puerto Rico, and from the upper 60s to mid 70s across lower elevations of the islands. Patchy fog can also be present during the overnight to early morning hours across sectors of interior Puerto Rico. With steering flow gaining a more easterly component, remnants of past frontal boundaries are forecast to move into the local islands from the east late Friday and into Saturday, promoting above normal, 1.5 to 1.9 in, precipitable water values and increased shower activity. Moisture in this value will persist into the end of the long term period. Limited flooding impacts continue to be possible during these days as available moisture increases and shower activity is steered into the area. && .AVIATION... (06Z TAFS) VFR conditions with mostly clear to partly cloudy skies will prevail. Increased cloud cover will focus along the Cordillera Central and southern PR after 13/16Z, with minimal to no operational impacts. Winds will be light to calm and variable overnight, shifting from the NE and increasing to 10-12 knots with sea breeze variations after 13/14Z, weakening after 12/23Z. && .MARINE... A surface high-pressure moving eastward across the western Atlantic will promote light to moderate northeast winds over the next few days. While current long-period northerly swells are subsiding, additional pulses are expected by Tuesday and will once again deteriorate marine conditions up to Small Craft Advisory criteria as they spread across the Atlantic waters and local passages during the second half of the workweek. && .BEACH FORECAST... While current long-period northerly swells are subsiding, additional pulses are expected tomorrow, maintaining deteriorated coastal condtions. A High Risk of Rip Currents will be in effect today throughout the workweek for the beaches of northern Puerto Rico, from Rincon to Fajardo, Culebra, St. Thomas and St. John. A High Risk of Rip Currents is also forecast for St. Croix by tomorrow night and last throughout the workweek. A High Surf Advisory will possibly be issued for some exposed areas as we approach the middle of the workweek. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Thursday afternoon for PRZ001-002- 005-008-010-012. VI...High Rip Current Risk through Thursday afternoon for VIZ001. AM...Small Craft Advisory from noon Tuesday to 6 PM AST Thursday for AMZ711. && $$ SHORT TERM...ICP LONG TERM....MRR
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