textproduct: Seattle/Tacoma

SYNOPSIS

A surface low will move southwest to northeast today bringing increasing winds to the area. High pressure will build in tonight with winds easing quickly. Upper level trough will move through today as well bringing showers and a chance of thunderstorms. The trough will move east tonight with drying northwesterly flow aloft. Upper level trough digging offshore with split flow aloft off the coast for a dry weekend. Flow aloft becoming zonal Monday with a chance of rain in the forecast at times next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Satellite imagery does not look like the last week of September. Cold front east of the metro area early this morning with a bent back occlusion off the coast. Steady rain ended a little after midnight over the interior. Doppler radar has shower activity over the northern portion of the area. Temperatures at 3 am/10Z were in the lower to mid 50s.

Lots of changes to the forecast this morning. The big question is where is the surface low off the coast associated with the bent back occlusion going to track. Previous model runs had the low moving inland south tracking through the Southwest Interior this morning. There are model solutions tonight that are sticking with this scenario. Surface observations along the coast show the strongest surface pressure falls not near the mouth of the Columbia River but instead between Hoquiam and buoy 41. This brings the low inland on a more northerly track with the low center taking aim at the Central Puget Sound later this morning. Strong surface pressure rises behind the low plus an unstable air mass possibly mixing 925 mb winds in the 30 to 40 knot range down to the surface will create windy conditions south of the low center. Have issued wind advisories beginning later this morning and continuing through the afternoon hours from Tacoma southward including the coast. In general expect west to southwest winds gusting 35 to 45 mph with a little stronger gusts along the coast. With plenty of foliage still on the trees, winds this strong could bring down some branches and cause power outages. This isn't the only wind scenario for the area today. As the low continues to move northeast this afternoon surface gradients will rapidly increase through the Strait of Juan de Fuca. Westerly wind surge coming down the Strait this afternoon will be strong enough to produce wind advisory strength wind gusts along the shores of the Strait of Juan de Fuca into Whidbey Island, especially the northern end. A wind advisory has been issued for these locations as well. Unstable air mass moving over the area this morning with an upper level trough over the area. Showers with a slight chance of thunderstorms for most of the day. There will be a quick very strong convergence zone somewhere between Seattle and Everett this afternoon. Thunderstorm chances are higher in the convergence zone. High temperatures in the upper 50s to mid 60s.

Wind advisory strength westerlies continuing into the early evening hours through the Strait into Whidbey Island. For the remainder of the area weather calming down with surface high pressure building into the area and the upper level trough moving off to the east. Winds through the Strait will ease before midnight. Clearing skies will produce the coldest morning since early June with lows in the 40s.

Saturday and Sunday looking dry at this point. Upper level trough offshore digging south with split flow aloft off the coast. Light surface gradients bring up the possibility of morning fog especially Sunday. Even with sunshine, highs will be below normal, in the lower to mid 60s. Sunday morning will be another cool one with the colder locations getting into the upper 30s. Felton

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Upper level trough moving inland Monday with the flow aloft consolidating off the coast. Models in pretty good agreement with the next system arriving Monday night or Tuesday bringing a chance of rain back to the forecast. Models solutions start to lose their consistency Wednesday and Thursday. Some of the solutions build a weak upper level ridge over the area while other solutions bring a weak system through Wednesday night or Thursday. Will have chance or slight chance pops both days until model solutions consolidate. Highs remaining in the lower to mid 60s with lows in the mid 40s to lower 50s. Felton

AVIATION

A surface low pressure system will continue to northeast across the terminals today. The center of the low will track from southwest Washington into Puget Sound through the day, bringing an occluding front through. The first bands of rain are moving through the Cascades and the north interior, with additional wrap around moisture on the west side of the low offshore this morning along the coast. This will move inland into the afternoon, with activity becoming more showery in nature. There remains a 20-25% chance of thunder for all the terminals today. Ceilings will gradually lower this morning with a mix of MVFR ceilings for Puget Sound, and outside areas seeing IFR to LIFR ceilings. Some mist will likely accompany the low ceilings. Improvement will likely prolong into late this afternoon with additional rain moving through - with models hinting 21-00Z for VFR improvement in the central/south interior only. Models are indicating widespread LIFR conditions Saturday morning, especially in the interior.

Winds will become increasingly gusty this morning, starting out of the southwest and becoming more westerly on the backside of the low. Sustained winds of 15-20 kt with gusts up to 30 to 35 kt are expected, particularly in the south interior, Pacific Coast, and Whidbey Island/Salish Sea Coast. Isolated wind gusts over 40 kt are possible in the Strait of Juan de Fuca. The winds will decrease Friday night into Saturday to 5 kt or less.

KSEA...Ceilings will decrease to MVFR this morning with areas of mist behind the first round of rain. The next round of rain will move through late this morning and afternoon and will be more showery in nature. There remains a 20% chance of thunder through the day. VFR improvement will take place later in the day (00Z). There are increasing chances for LIFR conditions Saturday morning from 12Z- 18Z. Winds will pick up after 18Z to 10-15 kt with gusts to 25 kt out of the southwest through 06Z, decreasing to 5 kt out of the south Saturday morning.

HPR

MARINE

A surface low pressure and frontal system is tracking through the coastal waters this morning, with the center of the low just off of Astoria OR. Radar has an area of thunderstorms around the center of the low moving to the northeast. Additional thunderstorms will be possible today in the coastal and interior waters as the system tracks northeastward.

With pressure drop observations at buoy 41 this morning (2 mb an hour) and high-resolution models indicating stronger winds, the gale warning was expanded to include all of the coastal waters for today. The gale warning continues for the Strait of Juan de Fuca, and the small craft advisory in the interior waters now includes the Admiralty Inlet. The strongest winds this morning will be in the southern coastal waters where gusts up to 40 kt are expected as winds increase out of the northwest behind the low. A strong push in the Strait of Juan de Fuca will also bring west wind gusts up to 40 kt later this afternoon and evening. The remaining Puget Sound/North Interior waters will see winds increase late this morning and afternoon, though confidence remains for only seeing small craft impacts in these waters.

Winds will decrease tonight into the weekend, with high pressure building offshore. A weak front will dissipate off the coast Sunday, with a stronger system moving through the waters midweek next week with another chance of hazardous winds and seas.

Seas will increase today to 9-12 ft with a couple instances of 13-15 ft with the highest winds. The seas will drop to 4-6 ft this weekend into early next week, but increase back to near 10 ft with the midweek system.

HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 10 AM this morning to 5 PM PDT this afternoon for Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Southern Hood Canal-Willapa and Black Hills.

Wind Advisory from 11 AM this morning to 8 PM PDT this evening for Eastern Strait of Juan de Fuca-Island County-Northern Washington Coast-Port Townsend Area-Western Strait of Juan de Fuca.

Wind Advisory from 6 AM this morning to 5 PM PDT this afternoon for Grays Harbor County Coast.

PZ...Gale Warning from 8 AM this morning to 5 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 11 AM this morning to 5 AM PDT Saturday for Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory from 11 AM this morning to 11 PM PDT this evening for Admiralty Inlet-Puget Sound and Hood Canal.

Gale Warning until 8 PM PDT this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.