Trades will continue through the next several days, gradually increasing in speed by mid-week next week, maintaining typical windward and mauka showers. A weak upper-level disturbance approaches the islands early next week, resulting in a possible uptick in moisture across windward slopes. This will be short- lived, however, and steady trades will return again for the remainder of the forecast period.
Latest radar imagery continues to display isolated windward showers riding on a prolonged trade wind pattern under a high pressure system anchored to the north of the Hawaiian Islands. Moderate to locally breezy trades will veer slightly from the northeast to a more easterly pattern this morning, gradually increasing in speed by mid-week, and then persisting through the remainder of the forecast period. This will help maintain typical trade showers across windward and mauka areas, though any precipitation associated with these showers is expected to remain light.
Global model guidance preserves the likeliness of a weak upper- level disturbance shifting over the islands as early as Monday, effectively increasing the moisture content across the windward slopes of most islands. This uptick in moisture may lead to some stronger showers due to instability from colder air aloft. Model precipitable water (PWAT) normalized anomalies show an increase from near normal to 1 to 2 standard deviations above normal from Monday to Wednesday, falling back to near normal. Trades will re- establish shortly thereafter, prevailing through the remainder of the week.
A high pressure system far north of the Hawaiian Islands will keep moderate to locally breezy easterly trade winds in the forecast through Sunday. An upper level disturbance will produce bands of showers riding into windward island mountains on the trade winds, expect periods of showers mainly over windward mountain areas favoring the overnight to early morning hours. Periods of MVFR conditions are expected through Sunday along windward mountain slopes due to low clouds and showers.
AIRMET Sierra in effect for mountain obscurations along north and east slopes of the Big Island of Hawaii. This AIRMET may need to expand in coverage to other islands later this morning.
A ridge of high pressure far north of the state will maintain moderate to breezy trade winds through today. A slight decrease is expected tonight into early next week as a weak trough passes through the state. The trough should bring an increase of shower coverage especially over windward waters. High pressure will rebuild far north of the state towards the middle of next week, which should bring the return of moderate to locally strong trades.
A small medium period NW swell continues to fill in this morning and will be reinforced by a larger NW swell filling in tonight. This reinforcing NW swell should peak on Sunday, then gradually decline through early next week. A developing hurricane-force low this weekend near the Aleutian Islands should send a moderate northwest swell towards the middle of next week.
Local nearshore buoys such as the Mokapu buoy is showing a modest increase of short-period energy from the NE this morning associated with a small fetch of strong winds few hundred miles NE of the state the past few days. This should provide a short-lived increase along east facing shores through this morning then gradually decline into Sunday. Otherwise, below average surf is expected along eastern exposures into next week due to the lack of any strong trade wind activity over and upstream of the state. Locally strong trade winds could return during the second half of next week, which could bring rough and choppy surf with near normal wave heights by the later half of next week.
Small background energy from the west will continue to linger through today and fade out on Sunday. A small southwest bump from the Tasman Sea that passed across the American Samoa 51209 buoy Wednesday is expected to slowly fill in today and peak on Sunday. No significant south swell is expected through the first half of next week. A fetch of gales passing east of New Zealand today could produce a small south-southwest swell for next weekend.
None.
