AFDSJU Area Forecast Discussion National Weather Service San Juan PR 318 AM AST Sat Apr 4 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, HYDROLOGY... .KEY MESSAGES... Updated at 318 AM AST Sat Apr 4 2026 * Breezy to locally windy conditions and a fading northeasterly swell will persist through early next week, leading to hazardous marine conditions and the formation of life-threatening rip current along northern and eastern beaches. * Above-normal moisture and increasing instability will support periods of heavy rainfall through midweek. * Elevated flooding risk, especially across windward areas overnight and interior/western Puerto Rico each afternoon. * Warmer-than-normal temperatures will develop by midweek, with heat indices potentially reaching the low 100s. && .Short Term(Today through Monday)... Issued at 318 AM AST Sat Apr 4 2026 Fair weather prevailed today across the islands, with passing showers across the local waters and moving inland across the windward sections in PR and the USVI occasionally. The easterly winds were mainly 10 or less, with land-breeze variations, especially along the leeward sections. Most coastal and urban sites recorded minimum temperatures in the low or mid-70s, while mountain sites recorded maximum temperatures in the low 60s. A surface high-pressure system over the central Atlantic will maintain an east to southeast wind flow across Puerto Rico and the U.S. Virgin Islands. This will result in breezy to locally windy conditions, with low-level winds generally between 15 and 20 knots. Under this surface regime, moisture levels will remain near or above climatological normal (with precipitable water (PWAT) values ranging from 2.0 to 2.2 inches, near or above the 75th percentile), supporting the development of trade wind showers. These showers will primarily affect windward locations each day, especially during the overnight and early morning hours, from late tonight into Sunday, and again from Sunday night into early Monday. A mid- to upper-level trough will gradually increase instability, with 700-500 mb lapse rates approaching 6.0-6.5 C/km. Combined with mid-level humidity between 70 and 90 percent, this environment will support efficient rainfall processes with some isolated thunderstorms between the afternoon and evening hours. By Sunday into Monday, this trough is expected to extend into the upper levels across or near the northeastern Caribbean, further enhancing atmospheric instability across Puerto Rico and the U.S. Virgin Islands. This evolving pattern will favor periods of trade wind showers during the overnight and morning hours, particularly across windward areas. When combined with low-level convergence, these showers could produce locally heavy rainfall and increase the risk of flooding in these regions. During the afternoon and evening hours, strong convective development is expected across interior and western Puerto Rico, with additional impacts possible across eastern Puerto Rico and the U.S. Virgin Islands. Overall, this pattern supports an elevated risk of flooding rainfall in the short term. Beach forecast Confused seas are creating life-threatening rip currents along north-facing beaches of Puerto Rico and the U.S. Virgin Islands, where entering the water is strongly discouraged. While south- facing beaches have a lower risk, caution is still advised as conditions can change quickly. && .Long Term(Tuesday through Saturday)... Issued at 318 AM AST Sat Apr 4 2026 A wet and unstable pattern will prevail across the region through much of the long-term period, as a mid- to upper-level trough approaches from the west and settles across the northeastern Caribbean. At the surface, an induced inverted trough near Hispaniola will maintain a persistent southeasterly wind flow across the region. This will promote the advection of abundant tropical moisture into the forecast area, with precipitable water (PWAT) values increasing to near or above 2.0 inches and moisture deepening through the entire column. This southeasterly flow will also support above normal temperatures, with model guidance indicating 925 mb temperatures increasing to near two standard deviations above climatological normals by midweek. As a result, warmer-than-normal conditions are expected at the surface, with heat indices potentially reaching the low 100s for the first time this year in some areas. In addition to the heat impacts, the increased low-level warmth will contribute to greater instability, providing additional fuel for convective development. Aloft, the presence of the upper-level trough will further enhance instability, with low- to mid-level lapse rates becoming modestly steep for the region. Combined with elevated relative humidity values through the 850-500 mb layer, this will support the development of heavy showers and widespread convective development. Under this pattern, scattered to numerous showers and thunderstorms are expected each day, with activity becoming more widespread during the afternoon hours due to diurnal heating and local effects. The most active period is anticipated Wednesday through Thursday, when the combination of peak moisture, anomalous warmth, and upper-level support will maximize convective coverage. Thunderstorms during this period will be capable of producing heavy rainfall, frequent lightning, and gusty winds. The available heat and instability may also support stronger thunderstorm development, with the potential for intense downpours. As a result, the risk of urban and small stream flooding will remain elevated, along with the potential for rapid river rises. Saturated soils and elevated streamflows from previous rainfall will further exacerbate flooding impacts, particularly across flood-prone and poor drainage areas. By Friday onwards, conditions are expected to gradually improve as the upper-level trough weakens and shifts away from the region. Although lingering moisture will continue to support isolated to scattered shower activity, a reduction in overall coverage and intensity is expected, with a transition toward more typical trade wind conditions by late in the period. && .AVIATION... (06Z TAFS) Issued at 318 AM AST Sat Apr 4 2026 Mainly VFR conditions expected, with brief MVFR/IFR conditions possible in SHRA/TSRA. Trade wind showers will impact eastern terminals overnight, while afternoon convection (04/16-23z) may affect interior and western Puerto Rico as well as windward terminals, including TJBQ and TJSJ. Expect calm to light and VRB winds thru 04/13z, then winds from the east to southeast at 10-16 kt with higher gusts. Mountain obscurations likely during periods of heavier showers and TSRA. && .MARINE... Issued at 318 AM AST Sat Apr 4 2026 Hazardous marine conditions are expected to persist through next week. A strong high-pressure system in the Atlantic will maintain fresh to locally strong easterly winds today, veering east-southeast late this afternoon through Sunday. When combined with a subsiding northeasterly swell, seas will remain choppy to rough, particularly across Atlantic waters and local passages. Consequently, Small Craft Advisories remain in effect for the Atlantic offshore and coastal waters, including the Anegada and Mona Passages through Sunday afternoon. While trade wind showers continue across the region, expect isolated to scattered thunderstorms during the afternoon hours over coastal waters, especially near western and northwestern Puerto Rico. Coverage may increase slightly over the weekend as an upper-level trough arrives, interacting with abundant tropical moisture. && .BEACH FORECAST... Issued at 318 AM AST Sat Apr 4 2026 Beaches across northern and eastern Puerto Rico, including Vieques, Culebra, and the U.S. Virgin Islands will remain hazardous for beachgoers throughout the weekend and into early next week. A subsiding northeasterly swell continues to spread across Atlantic waters and passages, with breezy to locally windy conditions along the coasts. Given these conditions, a High Rip Current Risk remains in effect for northern and eastern beaches of the islands through Sunday afternoon. Beachgoers and inexperienced surfers are strongly urged to avoid entering the water or walking on rocks and jetties, as life-threatening rip currents are highly likely. Always heed the advice of lifeguards and pay close attention to beach patrol flags and signs. && .HYDROLOGY... Issued at 318 AM AST Sat Apr 4 2026 Hydrologic conditions will become increasingly favorable for flooding impacts through much of the forecast period. Elevated moisture (PWAT 2.0 inches), increasing instability, and efficient warm-rain processes will support periods of heavy rainfall. Flooding is not expected to be widespread; however, there is an elevated risk of urban and small stream flooding, especially in areas experiencing repeated or slow-moving showers. The highest risk will occur overnight across windward areas and during the afternoon across interior and western Puerto Rico. Recent rainfall has resulted in saturated soils across portions of eastern and northern Puerto Rico, increasing runoff efficiency and the likelihood of rapid rises in streams and rivers, particularly in steep terrain. The flooding risk is expected to increase from this afternoon through midweek, with the potential for isolated flash flooding, especially during the peak period from Wednesday through Thursday. Conditions should gradually improve late in the week as moisture decreases and instability weakens. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Sunday afternoon for PRZ001-002- 005-008-010-012-013. VI...High Rip Current Risk through Sunday afternoon for VIZ001-002. AM...Small Craft Advisory until 6 PM AST Sunday for AMZ711-712-716- 723-741. Small Craft Advisory until noon AST Sunday for AMZ742. && $$