Coastal Flood — Kenai Peninsula, Alaska

2024-11-16 to 2024-11-17 · Kenai Peninsula, Alaska

Event narrative

A Gulf of Alaska low, centered south of Prince William Sound, was on a southeasterly track over the course of the November 16-17, 2024 period. With this low in place, a strong down (Cook) Inlet flow kept each day's strongest winds focused south of the Kenai Peninsula. However, due to the north and west nature of the overall flow, these perpendicular winds over the Alaska Range led to a lee-side low forming over the Cook Inlet. This led to lower barometric pressure over the Cook Inlet than would have been noted there otherwise. The primary evidence of how this low affected area winds can be seen on Synthetic Aperture Radar (SAR) satellite imagery on both the 16th and 17th, as Tuxedni Bay gap winds spilled out across the Inlet and towards Ninilchik. The SAR image taken the 16th, was only able to capture winds around 23 mph near Ninilchik's shoreline; the image taken the 17th was able to capture Tuxedni Bay

winds reaching 46-52 mph at its core. As there was little change in the overall pattern between the 16th and 17th, it can be inferred that strong Tuxedni Bay winds persisted over the course of the 2 day period, before finally diminishing in strength the 17th as the lee-side low transitioned eastward.

These Tuxedni Bay winds were likely able to drive any increased wave heights produced by a strong down-Inlet flow, into Ninilchik's shores; unfortunately, no buoy exists in the Cook Inlet north of buoy 46108 (along outer Kachemak Bay) to illustrate whether heightened waves were able to reach Ninilchik's shoreline.

The astronomical high tides reached 24.28 feet on November 16th, and 23.66 feet the 17th. Increased wind gusts were observed before the highest tide, as west-northwest winds were noted around 12 mph with gusts to 21 mph leading up to, and through, the high tide period at the Ninilchik wind sensor (sensor NRBA2). As this sensor is located a half-mile inland and sheltered by trees, the sensor located along Anchor Point's shoreline may provide an idea of potential wind strength along Ninichick's shore, about 20 miles to the north. Anchor Point observed sustained north-northwest winds around 25 mph, with gusts up to 35 mph for a prolonged 21-hour period (sensor APXA2) November 16th and 17th.

As it can be inferred that the winds recorded at Anchor Point may have also affected Ninilchik's shoreline, the SAR imagery noted in Figures 3 and 4 also speak to the likely event that Tuxedni Bay westerly gap winds influenced Cook Inlet wave activity during the two-day period; the assumption being that the Tuxedni Bay westerlies were likely able to bend down-Inlet waves into Ninilchik's shores. However, as winds diminished in strength and turned east by the 17th, it is likely that wave strength was weakened along Ninilchik's shoreline. Without any nearby buoy, precise wave information along Ninilchik's shoreline is lacking.

The Ninilchik community reported damage to Airport Road next to the boat harbor.

Wider weather episode

An area of strong winds developed along the CookInlet Saturday, November 16 and Sunday, November 17, 2024, wedged between a Gulf ofAlaska low pressure system centered just south of Prince William Sound, and a ridge of highpressure over the Bering Sea. In two unique regions of the Cook Inlet, local winds were enhanced by a disturbancewithin this flow aloftas it crossed the Alaska Range and moved over the Cook Inlet. Near Ninilchik, this disturbanceled to the development of a lee-side area of low pressure over the Inlet, which then enhancedcross-Inlet winds out of Tuxedni Bay, towards Ninilchik, affecting its coastline. Further south, a weak frontal boundary moving north out of the outer Kachemak Bay, resulted in several hours of strong southwesterly winds that combined with the peak high tide of the day of about 23 feet. In each case, high surf conditionsthat lasted hours to days, lead to extensive erosional damage both the Ninilchik'sandHomer Spit'scoasts.

Source: NOAA Storm Events Database, event_id 1221004. Narrative written by the NWS forecast office that issued the report.