Mona Passage Southward to 17N Marine Forecast
| Today...East Winds 10 To 15 Knots, Becoming Northeast 5 To 10 Knots Early This Afternoon, Then Increasing To 10 To 15 Knots Late. Seas 4 To 5 Feet. Wave Detail: East 4 Feet At 7 Seconds And North 2 Feet At 9 Seconds. Isolated Showers This Morning. Scattered Showers With Isolated Thunderstorms Late. |
| Tonight...Northeast Winds 10 To 15 Knots With Gusts Up To 25 Knots. Seas 4 To 5 Feet. Wave Detail: Northeast 4 Feet At 7 Seconds And North 2 Feet At 9 Seconds. Scattered Showers. |
| Tuesday...Northeast 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. Wave Detail: Northeast 4 Feet At 7 Seconds And North 2 Feet At 8 Seconds. |
| Tuesday Night...Northeast Winds 5 To 10 Knots. Seas 3 To 4 Feet. Wave Detail: Northeast 3 Feet At 8 Seconds. Scattered Showers. |
| Wednesday...East Winds 5 To 10 Knots. Seas 2 To 4 Feet. Wave Detail: Northeast 3 Feet At 8 Seconds. |
| Wednesday Night...Northeast Winds 5 To 10 Knots, Becoming East 10 To 15 Knots After Midnight. Seas 2 To 4 Feet. Wave Detail: Northeast 3 Feet At 8 Seconds. Scattered Showers. |
| Thursday...Northeast Winds 10 To 15 Knots. Seas 2 To 4 Feet. |
| Thursday Night...Northeast Winds 10 To 15 Knots. Seas 3 To 4 Feet. Scattered Showers. |
| Friday...East Winds 10 To 15 Knots. Seas 3 To 4 Feet. Scattered Showers In The Morning. |
| Friday Night...East Winds 10 To 15 Knots. Seas 3 To 5 Feet. Winds And Seas Higher In And Near Thunderstorms. |
| Area Forecast Discussion National Weather Service San Juan PR 540am AST Monday Dec 1 2025 .Short Term(Today through Wednesday)... Issued at 537am AST Monday Dec 1 2025 East-northeast trade winds brought passing showers across exposed coastal areas of the U.S. Virgin Islands and northern and eastern Puerto Rico, with a few reaching inland and leaving around half an inch of rain in isolated spots of northeastern Puerto Rico. Winds were influenced by the land breeze but still tended to come from the east-northeast at 5 to 10 mph, while many inland locations remained light or calm. Overnight temperatures dropped into the low 60s in the higher elevations, with upper 70s across the lower elevations. Today, strong winds aloft will provide just enough lift to help clouds grow and allow a few heavier showers to form. A shortwave trough moving in from the west will add a little more support later in the day. At the surface, winds will continue to weaken and turn from ENE to NE as a surface trough approaches from the east. Moisture will stay close to normal but will remain uneven across the area. Passing trade-wind showers will continue this morning across northern and eastern Puerto Rico and the U.S. Virgin Islands, but they will become less frequent through the day. As the day progresses, showers will form over land, mainly downwind from the mountains and where the sea breeze is strongest. This includes areas west-southwest of the islands and the Sierra de Luquillo, with the most active weather expected in southwest Puerto Rico. One or two isolated thunderstorms may form, but overall activity will stay limited. Hazard summary for today: a limited lightning risk and a low to no flooding risk, even if a thunderstorm develops. Tonight, winds will continue to weaken as a surface trough moves in from the east and the shortwave trough aloft gets closer. This will make the environment slightly more favorable for thunderstorms, though most activity should stay offshore. A few trade-wind showers may still reach northern and eastern Puerto Rico and the U.S. Virgin Islands, but they will be less frequent due to the lighter winds. On Tuesday, the shortwave trough will move over the area, bringing the coolest air aloft along with added instability and very weak steering flow from the surface trough. These conditions make Tuesday the most favorable day for thunderstorms, even if they remain limited in coverage. Slow-moving showers or storms could bring heavy rain, causing ponding of water or minor urban flooding. Tuesday night, a few storms may linger or develop offshore under the influence of the trough. By Wednesday, the trough will move away and a mid-level ridge will build in, bringing warmer and drier air aloft and a more stable pattern. Thunderstorm chances will drop sharply, leaving only a small chance of one or two isolated afternoon showers or storms. Hazard summary: limited lightning risk increasing tonight and peaking Tuesday, with a limited flood risk also increasing Tuesday; both risks lower on Wednesday. .Long Term(Thursday through Monday)... Issued at 537am AST Monday Dec 1 2025 The long-term forecast remains without significant changes. An upper-level trough will continue to influence the region by Thursday, while an easterly disturbance approaches the islands, sustaining a humid and somewhat unsettled pattern. Latest precipitable water (PWAT) guidance shows moisture peaking Thursday between 1.65 and 1.85 inches, which is above the climatological norm for early December. This enhanced moisture will support showers driven by a northeasterly flow, periodically affecting windward areas. Afternoon convection is also possible, particularly across interior and western Puerto Rico, where brief heavy downpours and isolated thunderstorms cannot be ruled out, but the 500 mb temperatures should warm to above-normal values and that might slightly decrease the chance. As a result, this period (Thursday) feature the highest precipitation chance, posing a limited flood risk at this time, as rain activity will likely result in ponding of water in roads and poorly drained areas, and a low chance to observe urban and small streams flooding. Winds are also expected to become breezier from Thursday through the weekend. By Friday and into the weekend, a high-pressure system over the western Atlantic will move north of the islands. As ridging builds at various levels of the atmosphere, more stable conditions are expected, with drier air arriving and PWAT (Precipitable Water) values falling below 1.4 inches, accompanied by moderate to locally breezy easterly to northeasterly winds. Even so, lingering moisture (20 to 50 percent chance of showers) will continue to support occasional showers, especially during the overnight and early morning hours. Temperatures at 925 mb are forecast to be near-average values, supporting seasonal surface temperatures. No heat-related risks are anticipated at this time. Marine Issued at 530am AST Monday Dec 1 2025 A surface trough east of the islands will promote moderate northeasterly winds today, allowing seas to subside slightly but still supporting the small craft should exercise caution headline, particularly across the offshore Atlantic waters. As this feature approaches and moves across the CWA (County Warning Area) around Tuesday, winds will become gentle to moderate from the east to southeast, then shift to moderate from the east to northeast late Wednesday night. Isolated thunderstorms will be possible across the waters over the next few days. Beach Forecast Issued at 530am AST Monday Dec 1 2025 Along the north and east facing beaches of Puerto Rico, including Vieques and Culebra, and the U.S. Virgin Islands, there is a moderate risk of rip currents today. These conditions are expected to remain similar through the workweek, with some improvement as winds diminish, particularly on Tuesday and Wednesday. Beachgoers are urged to use caution, as a moderate risk means life- threatening rip currents are possible in the surf zone. A low risk persists elsewhere; however, even with a low risk, dangerous rip currents can still develop near groins, jetties, reefs, and piers. Visitors and residents are encouraged to always swim near a lifeguard. For location-specific details, visit weather.gov/beach/sju. In addition to rip currents, beachgoers should remain weather aware, as showers and isolated thunderstorms may move across coastal areas of the islands. .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...Small Craft Advisory until 6am AST early this morning for AMZ711. |
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