Mona Passage Southward to 17N Marine Forecast
| Tonight...East Winds 10 To 15 Knots, Increasing To 15 To 20 Knots After Midnight. Seas Around 4 Feet, Occasionally To 5 Feet. Wave Detail: East 4 Feet At 7 Seconds And Northeast 1 Foot At 12 Seconds. Scattered Showers With Isolated Thunderstorms. |
| Sunday...East Winds 10 To 15 Knots With Gusts Up To 25 Knots. Seas 4 To 5 Feet, Occasionally To 6 Feet. Wave Detail: East 4 Feet At 6 Seconds And Northeast 1 Foot At 12 Seconds. Scattered Showers. |
| Sunday Night...East Winds 10 To 15 Knots, Increasing To 15 To 20 Knots After Midnight. Seas 4 To 5 Feet, Occasionally To 6 Feet. Wave Detail: East 4 Feet At 7 Seconds And North 1 Foot At 12 Seconds. Scattered Showers In The Evening. |
| Monday...East Winds 10 To 15 Knots With Gusts Up To 25 Knots. Seas 4 To 5 Feet, Occasionally To 6 Feet. Wave Detail: East 5 Feet At 6 Seconds And North 1 Foot At 12 Seconds. |
| Monday Night...East Winds 10 To 15 Knots With Gusts Up To 20 Knots. Seas 3 To 4 Feet, Occasionally To 5 Feet. Wave Detail: East 4 Feet At 7 Seconds And North 1 Foot At 11 Seconds. Scattered Showers. |
| Tuesday...East Winds 10 To 15 Knots With Gusts Up To 20 Knots, Diminishing To 5 To 10 Knots In The Afternoon. Seas 3 To 4 Feet, Occasionally To 5 Feet. Wave Detail: East 4 Feet At 7 Seconds And Northeast 1 Foot At 11 Seconds. Scattered Showers In The Morning. |
| Tuesday Night...East Winds 10 To 15 Knots With Gusts Up To 20 Knots. Seas 3 To 4 Feet, Occasionally To 5 Feet. Scattered Showers. |
| Wednesday...East Winds 10 To 15 Knots, Diminishing To 5 To 10 Knots In The Afternoon. Seas 2 To 3 Feet. Scattered Showers In The Afternoon. |
| Wednesday Night...East Winds 10 To 15 Knots. Seas 3 To 4 Feet, Occasionally To 5 Feet. |
| Thursday...East Winds 5 To 10 Knots. Seas 3 To 5 Feet, Occasionally To 6 Feet. |
| Thursday Night...East Winds 5 To 10 Knots. Seas 3 To 5 Feet, Occasionally To 6 Feet. Winds And Seas Higher In And Near Thunderstorms. |
| Area Forecast Discussion National Weather Service San Juan PR 226pm AST Sat April 18 2026 .Short Term(This evening through Monday)... Issued at 226pm AST Sat April 18 2026 A mid to upper-level trough and a surface high pressure system over the North Atlantic remain the dominant features across the region. Their interaction is promoting a moist, unstable, and breezy pattern. Combined with abundant moisture, diurnal heating, and local effects, this setup is supporting another active afternoon with showers and thunderstorms across interior, western, and northern Puerto Rico, extending into the San Juan Metro Area. Precipitable water values remain above normal, and although gradual drying aloft has begun, sufficient moisture and instability persist to support locally heavy rainfall. As typical, activity will transition from afternoon and early evening convection over land to a more advective pattern overnight, with showers moving across eastern Puerto Rico, the U.S. Virgin Islands, and surrounding waters on easterly winds. A gradual transition toward slightly drier and more stable conditions is expected as the upper-level trough shifts east, with subsidence developing in its wake while a mid-level ridge builds from the west Sunday into early next week. At the same time, a drier airmass will filter in from the northeast, with moisture becoming increasingly shallow and largely confined below 700–800 mb. Despite this, sufficient low-level moisture and daytime heating will support a typical diurnal pattern, with afternoon convection across interior and western Puerto Rico and passing showers overnight and in the morning. Partial morning clearing will promote heating, followed by afternoon convection and increasing cloudiness, with this pattern repeating through the period. Breezy easterly winds will persist, gradually weakening early next week as the surface high shifts and a frontal boundary approaches from the northwest. Across the U.S. Virgin Islands, rainfall will remain more variable, with lower confidence in coverage and intensity. The primary hazards will continue to be flooding, landslides, lightning, and rapid river rises. Soils remain saturated and rivers elevated, resulting in a low threshold for impacts. Persistent or repeated showers and thunderstorms may quickly lead to urban and small stream flooding, river rises, landslides, and isolated flash flooding. Saturated soils combined with gusty winds may also result in downed trees and power lines. Given ongoing activity this afternoon, impacts may develop rapidly. While conditions may gradually improve by Monday, localized hazards will persist where heavier rainfall occurs. Residents and visitors should remain alert, especially in flood-prone and mountainous areas, and monitor forecasts and warnings. .LONG TERM(Tuesday through Saturday)... Issued at 232am AST Sat April 18 2026 The current forecast remains consistent with the previous discussion, showing no significant changes. Drier and more stable conditions are anticipated to return as the influence of the short term period’s upper-level trough weakens and moves away from the region. A stable air mass will be present aloft due to a building mid-level ridge over the area. At the surface, a dominant high- pressure system over the central Atlantic will maintain light to moderate easterly winds through the middle of the week then becoming northeasterly and southeasterly at the second half of the week. Precipitable water (PWAT) values are expected to drop to normal values with high end normal to above normal values at times. Local weather will be seasonal with passing showers over windward sectors during the morning and afternoon hours. This will be followed by afternoon convective activity across the interior and W PR on Tuesday with steering wind variations prompting afternoon convection over SW PR on Wednesday and W-NW PR on Thursday and N PR on Friday and Saturday. The combination of available moisture, daytime heating, and local effects could lead to moderate to heavy rainfall and isolated thunderstorms during these afternoons. Temperatures at 500 mb are forecast to remain seasonal (-6 C to - 8 C), isolated thunderstorms are still possible, particularly to end the period due to a nearby mid to upper trough. Given previous rainfall, saturated soil, and elevated river levels, the potential for flooding remains. Temperatures at 925 mb will also stay seasonal throughout most of the period. Marine Issued at 226pm AST Sat April 18 2026 An unstable weather pattern across the regional waters will persist through Sunday. Periods of strong thunderstorms, particularly across the western waters of Puerto Rico are expected during the afternoon hours. A surface high pressure over the Atlantic will promote mainly moderate to fresh easterly winds across the offshore Atlantic waters and local Caribbean passages, resulting in moderate to locally choppy seas through the weekend. Small craft operators should exercise caution. A small northeasterly swell will also continue to propagate across the Atlantic waters and Caribbean passages through early next week. Beach Forecast Issued at 226pm AST Sat April 18 2026 There is a a moderate risk of rip currents along the north-facing beaches of Puerto Rico, Culebra, and the U.S. Virgin Islands and this pattern is is expected to prevail over the forecast period. This means that life-threatening rip currents are possible in the surf zones. Beachgoers are encouraged to remain cautious in these exposed areas. Another beach concern is the development of thunderstorms each afternoon, particularly along the northwestern beaches of Puerto Rico. Remain weather-aware due to rapidly changing conditions, and be prepared to seek shelter if you hear thunder. .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. |
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