textproduct: Honolulu

SYNOPSIS

Fronts passing north of the islands this week will maintain light to moderate east to east-southeast winds and dry conditions over the region. There is a chance early next week for unsettled weather with a front approaching from the northwest.

DISCUSSION

The forecast has been updated to reflect the latest solution of the National Blend of Models (NBM), but very little has changed in the forecast in the coming days.

A high pressure ridge north of the islands is being pushed southward by a front to the north. This is resulting in the weakening of the trades over the islands, and with additional fronts expected to pass north of the islands, the winds will remain on the light to moderate side into the weekend. A stable mid level layer and zonal flow in the upper levels will help maintain a relatively dry weather pattern in place over the next several days.

The next substantial weather feature is a stronger front that will approach the islands from the northwest this weekend. The latest global models runs indicate this front will stall out west of Kauai Sunday, before lifting northward. The GFS brings slightly more unstable air than the ECMWF towards the islands with this system on Sunday. However at this time, both models suggest that the unstable airmass will not impact the islands. Another frontal system could reach the western islands early next week. However with that system days away, will watch future models runs to see what impacts we might see from that system.

AVIATION

A ridge north of the state will sink south and weaken today as a front passes by to the north. Expect gentle trade winds over the western half of the state and more moderate trades over the eastern half. Terrain sheltered areas will likely see afternoon seabreezes in this lighter trade wind pattern. Expect mostly VFR conditions. Brief MVFR conditions could develop along windward and mauka regions and along sheltered leeward and interior areas during afternoon seabreezes.

No AIRMETs in effect and none are expected.

MARINE

A ridge of high pressure north of the state will gradually weaken and drift south over the islands on Wednesday. This will cause our current moderate to locally fresh easterly trade winds to gradually weaken over the next several days and veer from the southeast direction. The forecast beyond Thursday will be highly dependent on the evolution of a large North Pacific storm developing Thursday into Friday. Latest global models and its ensemble members are in line with a front approaching the state from the northwest Friday into Saturday with the front stalling and weakening within the vicinity of Kauai from Saturday into Sunday.

Although the details remain uncertain regarding thunderstorm chances, confidence is increasing for large seas building above the Small Craft Advisory (SCA) thresholds (10 ft or higher) this week. The first round of high seas will build in from Wednesday through Friday, and then another round of SCA conditions with the second larger northwest swell builds into the region from Saturday afternoon into Sunday.

The current northwest swell will continue to decline today. A large long period northwest (320-330 degree) swell will fill in starting later tonight through Wednesday, likely exceeding advisory thresholds through Thursday. This northwest swell could briefly approach warning thresholds late Wednesday night into Thursday morning.

A large storm force low is expected to develop across the West Central Pacific on Thursday and could send our first extra large northwest swell of the season into the islands from Saturday night into Sunday affecting exposed north and west facing shores. There are still some differences regarding the intensity of the low with each model run, but nonetheless we should see an extra large swell by next Sunday. Expect a higher degree of uncertainty on the final size of this next swell, as the size of the low and the close proximity of the fetch leaves some potential for even giant size surf affecting north and west facing shores by Sunday.

Surf along east facing shores will remain small through the week due to the lighter winds.

FIRE WEATHER

Winds and humidity levels will remain below critical fire weather thresholds this week. Brief passing showers will tend to favor island interiors during the afternoons and windward areas overnight into the early mornings.

HFO WATCHES/WARNINGS/ADVISORIES

None.