San Juan Islands and Northern Inland Waters Marine Forecast
| Tonight...Se Wind 15 To 25 Kt Rising To 20 To 30 Kt After Midnight. Wind Waves 3 To 5 Ft. A Chance Of Showers In The Evening. A Slight Chance Of Tstms. |
| Tue...Se Wind 15 To 25 Kt. Wind Waves 2 To 4 Ft. Rain In The Morning Then Showers And A Slight Chance Of Tstms In The Afternoon. |
| Tue Night...Se Wind 10 To 20 Kt Becoming 5 To 15 Kt After Midnight. Wind Waves 1 To 3 Ft. Showers And A Slight Chance Of Tstms. |
| Wed...E Wind 15 To 25 Kt Becoming Sw 5 To 15 Kt In The Afternoon. Wind Waves 2 To 4 Ft Subsiding To 2 Ft Or Less In The Afternoon. |
| Wed Night...S Wind To 10 Kt Becoming 5 To 15 Kt After Midnight. Wind Waves 2 Ft Or Less. |
| Thu...S Wind 5 To 15 Kt. Wind Waves 2 Ft Or Less. |
| Thu Night...Sw Wind 5 To 15 Kt Becoming W To 10 Kt After Midnight. Wind Waves 2 Ft Or Less. |
| Fri...Nw Wind To 10 Kt. Wind Waves 1 Ft Or Less. |
| Sat...Nw Wind To 10 Kt. Wind Waves 1 Ft Or Less. |
| Area Forecast Discussion National Weather Service Seattle WA 346pm PDT Monday September 25 2023 Synopsis A trough of low pressure over the Gulf of Alaska will swing a series of frontal systems into the region through mid week. Wet and occasionally breezy weather is expected. Then, a gradual transition to drier conditions is favorable towards the weekend as upper-level ridging builds. Short Term - Tonight Through Thursday 500mb analysis depicts a broad trough of low pressure over the Gulf of Alaska as it ushers strong SW flow into the region. In sharp contrast, ridging is experienced downstream over the Intermountain West. Closer to the surface, a stout 960mb surface low is portioned off the PNW and BC coast over the NE PAC. Its associated front has pushed well inland as steadier rain from this morning has become more showery in nature. A regime of steep low-level lapse rates (6-7.5 C/km) from the interior to the coastal waters along with upper-troughing providing PVA/synoptic scale lift within this post-frontal airmass will help to keep shower chances in the forecast through tonight. RAP analysis indicates meager SBCAPE values (100-500 J/kg) in the hours ahead so can't rule out a few thunderstorms for the remainder of the afternoon into the evening, especially along the coast. Along with showers, locally breezy winds are possible. Widespread 50s are in store for overnight lows. Rain showers and a slight chance (15%) of thunderstorms are again in the forecast for Tuesday and the remainder of the short term. The aforementioned upper-trough will continue to direct shortwave disturbances into our area perturbing the environment. A strong 150 kt jet streak in the 300mb levels will lead to favorable jet dynamics. Out of this the development of a compact low center over the open waters will track towards the WA/OR coast by Tuesday evening. Uncertainly exists in this low feature's exact track which in turn will lead to variations in wind forecasts. But, gusts up to 30-35 mph are currently possible along the coast with gusts up to 20-25 mph throughout the interior. As mentioned, rain and showers are likely through Thursday. The Storm Prediction Center has a general thunderstorm risk for most of western Washington on Wednesday and with a cool upper-trough directly overhead on Thursday, can't rule out an additional slight chance on this day if enough instability is present. 48-hr forecasted rainfall totals through Wednesday evening has 2.0-4.0" for the coast/Olympics, 0.50-1.50" throughout the lowlands and 1-3" for the Cascades. Highs will remain in the 60s with overnight lows in the 50s. Long Term - Friday Through Monday Ensemble forecasts (GEFS, EPS, and CMC) are all in agreement of an upper-level ridge building offshore on Friday before nosing into BC on Saturday. If the pattern remains on track we could see its influence as conditions may dry out over the weekend, allowing a brief reprieve from rainfall. However, ridging may flatten going into the beginning of next week. Here, we could see the pattern re- amplify as rain chances return. Slightly below normal temperatures are expected through the long term period. McMillian Marine A 960 mb low is currently centered west of the region but will begin to weaken and drift north tonight. A few isolated thunderstorms have developed over the coastal waters, but activity should diminish into tonight. Thunderstorms are again possible Tuesday. These thunderstorms do have the potential to produce a waterspout, but any should be weak and short-lived. Another low pressure system will develop overnight Tuesday and swing across the area Wednesday morning. Models differ on the exact track, but gusty winds and the potential for few thunderstorms in the coastal waters will be reinforced with this system. A weak low swings south of the region Thursday before high pressure returns and dominates into the weekend. Gale force winds over the coastal waters will back down to Small Craft Advisory levels tonight into Wednesday. Small Craft Advisory conditions continue for the Strait of Juan de Fuca, Admiralty Inlet, and the Northern Inland Waters until Tuesday afternoon. A brief period of gusty winds up to Small Craft criteria are possible Tuesday morning into the early afternoon for northern Puget Sound. Seas ranging from 15 to 20 ft will continue tonight Tuesday, then begin to quickly decline Wednesday into Thursday, where seas ease to 6-9 ft into the weekend. LH Hydrology Widespread rainfall amounts through Wednesday evening of at least 1-2" inches possible across the lowlands, 1-3 inches possible over the coast and Cascades, and 3-4 inches over the Olympic mountain river basins. River flooding is not currently forecast thanks to the dry antecedent conditions, but attention will need to be paid to the Skokomish and also for rainfall rates over burn scars. NOAA Seattle WA Office: Watches - Warnings - Advisories WA...None. PZ...Small Craft Advisory until 6pm PDT Tuesday for East Entrance U.S. Waters Strait Of Juan De Fuca Grays Harbor Bar. Small Craft Advisory until 6pm PDT Tuesday for Admiralty Inlet Central U.S. Waters Strait Of Juan De Fuca- Northern Inland Waters Including The San Juan Islands- West Entrance USA Waters Strait Of Juan De Fuca. Gale Warning until 2pm PDT this afternoon for East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 2am to 2pm PDT Tuesday for Puget Sound and Hood Canal Gale Warning until 6pm PDT this evening for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory from 6pm this evening to 6pm PDT Tuesday for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Gale Warning until 2am PDT Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory from 2am to 6pm PDT Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. |
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