textproduct: Anchorage

LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)

Key messages:

- A very strong low pressure system will develop over the Bering Sea between Wednesday and Friday.

- Strong winds, large waves and heavy rainfall are likely near this storm system across much of the Bering Sea, Pribilof Islands, and portions of Southwest towards the latter half of this week.

- A threat for coastal flooding will exist along the Southwest coast sometime between Wednesday evening and Saturday. The concern for significant coastal flooding has lessened (25% to 35% chance) due to the storm likely remaining farther south.

Discussion:

The interaction of a low in the Bering Sea and the remnants of typhoon Dujuan is the forecast challenge for the second half of this week through next weekend. What makes this system so complex is that the ex-Dujuan system will basically split its energy on Wednesday with a good potion of its moisture and heat being entrained into the Bering Sea low which will rapidly strengthen it. The other part of its energy will not get entrained and will track eastward, south of the Aleutian Islands. The amount of moisture that is absorbed into the Bering Sea low will determine how strong each low becomes. Attempting to resolve this is giving fits to all of the models whether they be deterministic, ensemble, or AI models. All are struggling with the track, timing, and strength of this intensifying Bering Sea low which is to be expected.

However, even in all this chaos, there are some things that look more likely than others. First, models are all backing off a the expected strength of this low. Yesterday they ranged from a minimum central pressure of 935 mb to 945 mb. Today that range is closer to 960 to 970 mb. That is a significant difference in strength and a strong, but not extreme system. Second, the track is trending farther to the south on just about all model types. This is very important for the threat of coastal flooding in the Kuskokwim Delta as the farther south the low tracks, the less likely coastal flooding will be. There remains a chance the low center track as far north as Nunivak Island on Thursday or Friday, which would be the worst scenario for Kuskokwim Delta storm surge. However, the more likely scenario is that the low center remains farther to the south and west which will keep winds from a southeasterly to northeasterly direction which would only put a few areas (such as Kwigillingok) at risk and only during southeasterly winds along the front.

The Aleutian Islands from Attu through Dutch Harbor will likely see the strongest winds in this storm. It is still too early to really nail down where and when the strongest winds will occur. However, with the anticipated weaker central pressure of the low, maximum gusts are expected to be in the 70 to 80 mph range which is lower than it looked like yesterday when the low looked like it would be stronger.

Even with these trends, there is still a chance the entire former typhoon gets absorbed into the Bering Sea low and intensifies stronger than it looks today. This will still be a large and strong low with rough weather even at a weaker strength, so this system bears watching closely for anyone with interests in Southwest Alaska or the Bering Sea region.

As for Southcentral and the Gulf of Alaska region: the low that track south of the Aleutians will make its way to the Gulf of Alaska region Thursday into Friday. As with the the Bering Sea low, this one has a high degree of uncertainty due to it still being uncertain how much of this storm's energy get entrained into the Bering Sea low. At this time, it does appear likely that a fairly strong front will move into the Gulf of Alaska by Thursday and bring rain and wind to the Gulf region. What happens next with this low, and whether it intensifies in the Gulf or weakens there, will be dependent on what happens with the Bering Sea low.

AVIATION

PANC...The next round of rain and MVFR ceilings arrives this evening and overnight as a low in the Gulf moves into the Prince William Sound. Showers with this round will persist through Monday morning. Ceilings are on track to lower to IFR throughout the morning hours as visibility ticks down to MVFR with any heavier showers. Expect mostly light and variable winds through Monday morning. Rain showers will continue through Monday afternoon with MVFR visibility and IFR ceilings.