AFDSJU Area Forecast Discussion National Weather Service San Juan PR 258 PM AST Tue Dec 23 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 246 PM AST Tue Dec 23 2025 * Marine and coastal conditions will deteriorate late tonight through the weekend as increasing northeasterly winds and multiple pulses of long-period northerly swell create choppy to rough seas and hazardous conditions for small craft. * Rip current risk will increase to high along exposed northern and eastern beaches of Puerto Rico, Culebra, and the USVI as northerly swell builds and persists through the end of the week. A High Surf Advisory cannot be ruled out. * A frontal boundary will pass tonight through early Thursday, increasing the frequency of showers, mainly overnight and during the morning hours. Rainfall amounts are expected to remain limited, with minor ponding of water on roads and in poorly drained areas possible. * Persistent northeasterly flow will keep temperatures seasonably cool to slightly below normal, particularly at night and across higher elevations. Patchy fog may develop late in the week during the late night and early morning hours, especially across interior and valley locations of Puerto Rico, leading to brief reductions in visibility. && .Short Term(This evening through Thursday)... Issued at 246 PM AST Tue Dec 23 2025 Passing showers persisted during the morning hours, mainly moving over the northern and eastern portions of Puerto Rico, including Culebra, as well as St. Thomas and St. John in the U.S. Virgin Islands. Based on WSR-88D rainfall estimates, some areas ranged between 1.0 and 1.5 inches. Minimum temperatures over urban and coastal areas remain in the low to mid 70s, with localized areas in the high 60s; On the other hand, higher elevations remained in the low to mid 60s. Breezy conditions also persisted, under a northeasterly wind flow, as stations reported wind gusts between 25 and 28 mph in the higher elevations and up to 34 mph detected by the San Juan buoy. These conditions are likely to continue throughout the day. No major changes were introduced to the short-term forecast, although tonight is forecast as the wettest day of the period. Satellite-derived products highlight an area of high moisture content associated to a frontal boundary north of the region, with PWAT values between 1.5 and 1.6 inches, near the above climatological normal. From the probabilistic guidance of the GFS and ECMWF, theres high confidence in increasing moisture content in the low and mid levels for this time of the year, with relative humidity between 70 and 80% in the low levels and 40 - 50% in the mid levels. Under a northeasterly wind flow, the frequency of showers should increase late tonight, moving over windward sections of the islands, some reaching interior portions of Puerto Rico. Although significant flooding is not expected, rainfall accumulations could lead to ponding of water over roadways, urban, and poorly drained areas, with a low chance of flooding. Based on the latest model guidance, moisture content will gradually decrease as a surface high pressure builds over the western Atlantic, weakening the frontal boundary. Nevertheless, a deep- layered trough will introduce instability to the forecast, with cooler than normal 500 mb temperatures (between - 9 and -10 degrees Celsius), favoring deep convection. Additionally, strong winds (250 mb winds between 70 and 80 kt) in the upper levels may allow ventilation and cloud growth. Hence, afternoon convection is expected across southwestern portions of Puerto Rico, then an advective cooling pattern with showers and isolated thunderstorms developing over the regional waters and moving over windward sections of the islands on Tuesday night (Christmas Eve) into early morning Wednesday (Christmas Day). Although widespread thunderstorms are not expected, isolated thunderstorms may produce localized flooding, gusty winds, and lightning. Hence, the flooding and lightning risk will remain limited. By Thursday afternoon, a drier air mass should filter into the region, limiting shower activity for the rest of the period. Under a northeasterly wind flow, cooler temperatures are expected across the islands, with minimum temperatures lower in elevations in the high 60s and mid 70s, and higher elevations in the mid 50s to low 60s. && .Long Term(Friday through next Monday)... Issued at 537 AM AST Tue Dec 23 2025 Drier air behind the frontal boundary will dominate throughout the the period. Precipitable Water (PWAT) values are forecast at around to below an inch with isolated patches of moisture (PWAT up to around 1.2 in) reaching the area and promote passing showers from time to time. Although low PWAT values are forecast, upper troughs will move northeast of the area during the latter part of this week. building surface high over the western Atlantic and a frontal low over the north-central Atlantic will promote northeasterly steering flow to start the period. Model guidance suggests that winds will gradually veer to start the next week, promoting southeasterly flow by the end of the period. Under the northeasterly flow, 925 mb temperatures are forecast to be below normal. Minimum temperatures are forecast in the 50s to low 60s across higher elevations of PR, in the upper 60s to mid 70s across lower elevations of PR, and in the low to mid 70s across the USVI. Maximum temperatures are forecast around the mid 80s across lower elevations of the islands, with isolated/urban areas a bit higher. This will likely enhance patchy fog across sectors of interior Puerto Rico. && .AVIATION... (18Z TAFS) Issued at 246 PM AST Tue Dec 23 2025 Most VFR conds expcd this aftn across all TAF sites. NE winds will reduce btwn 6 - 10 kt, becoming VRB at JPS. Tonight, -SHRA/+SHRA expcd over the northern terminals (JSJ, JBQ, JIX) particularly 24/03-06z, which may reduce CIGs/VIS, leading to MVFR conds through at least 24/12z. Although conds aren`t favorable, TSRA cannot be ruled out across these terminals. Winds will increase by 24/12-13z, around 15 kt with gusts up to 25 kt. VCTS is pssbl at JPS by 24/16-18z due aftn convection. && .MARINE... Issued at 246 PM AST Tue Dec 23 2025 Buoy 41043 is already indicating long-period NNE swell with periods near 14 seconds, confirming the arrival of a long-period northerly swell associated with the frontal low. This swell will spread across the offshore Atlantic waters late tonight, resulting in choppy to rough seas and hazardous conditions for small craft. Seas are expected to build to 6 to 9 feet, spreading into the nearshore Atlantic waters and local passages. Small Craft Advisories remain in effect; for additional information, refer to the Marine Weather Message (MWWSJU). Another pulse of northerly swell late in the workweek will support deteriorated marine conditions through the weekend. && .BEACH FORECAST... Issued at 246 PM AST Tue Dec 23 2025 The forecast remains on track, with conditions deteriorating this evening as a northerly long-period swell arrives. Buoy 41043 is already indicating long-period NNE swell with periods near 14 seconds. This swell will increase the risk of rip currents to high for exposed northern beaches by this evening and continue through the rest of the week. A High Surf Advisory may be required with this swell event, which could result in localized beach erosion and dangerous swimming conditions. Another pulse of northerly swell will arrive later in the workweek, supporting hazardous beach conditions through the weekend. For further information, refer to the Coastal Hazard Message (CFWSJU). && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk from 6 PM AST this evening through late Thursday night for PRZ001-002-005-008. VI...None. AM...Small Craft Advisory until midnight AST Thursday night for AMZ711. Small Craft Advisory from noon Wednesday to midnight AST Thursday night for AMZ712-716-723-741-742. && $$