Moderate trades will continue through Tuesday, bringing limited showers mainly windward and mauka. An upper level low will help weaken winds and turn them out of the southeast Wednesday, and showers will increase as moisture increases. Heavy rainfall may occur late Wednesday through Friday.
Isolated showers were occurring mainly windward and mauka early this morning, and trade winds were averaging 5 to 15 mph with a few gusts in the 20s. Skies were partly to mostly cloudy windward and mostly clear leeward.
We expect a relatively dry trade wind regime to continue through most of Tuesday. Showers will be confined mainly to windward and mauka locations. Wind speeds will be moderate, generally averaging 10 to 20 mph, with higher gusts. Late Tuesday, things may get more interesting.
The latest models continue to show a strong upper level low developing to our northwest late Tuesday night as a sharp trough cuts off. This will aid in the formation of a surface low approximately 900 miles to our northwest and turn our surface winds out of the southeast. As tropical moisture is brought northwest, PW values will increase to around 2" and dewpoints will rise to around 70 Thursday and into the lower 70s Friday. As this deeper moisture moves in, heavy rain will become likely. The exact trajectory of this moisture is not known with high confidence yet, but at this time it appears all the islands will be impacted. It will take a few more days for the models to converge on the location and evolution of the surface low, and that will help dictate where the moisture advection is maximized.
Moderate trades through the period. Windward and mauka SHRA possible. MVFR conds in SHRA otherwise VFR prevails.
AIRMET Sierra is in effect for mtn obsc for windward Big Island. Conds should improve in the mid morning hours.
High pressure north of the Hawaiian Islands will produce moderate to locally fresh trade winds through Monday. The Small Craft Advisory for the windier waters and channels around Maui County and the Big Island has been extended through Monday afternoon. After this point, high pressure to the north begins to weaken and trade winds will start to diminish. By Wednesday, troughing developing northwest of the islands are increasingly likely to cause winds to veer out of the southeast. This is likely to be accompanied by increased shower activity for the latter half of the week.
Surf along south-facing shores will remain below average today. Forerunners from a new small, long-period south swell arrive today and will slowly fill in tonight and Monday, with a peak slightly above seasonal averages Tuesday into Wednesday. For the latter half of the week, surf near or slightly below average will be maintained by this fading swell combined with a mix of new, small south swells.
Surf along north-facing shores becomes tiny today before another small, medium-period northwest swell arrives tonight and peaks on Monday, producing a small bump in surf lasting into Tuesday. Surf will continue to trend up for north shores as this will be followed by a slightly larger long-period northwest swell that peaks on Wednesday. Surf may approach moderate levels late week as medium-period northwest swell energy further increases. Surf along east facing shores will be choppy through Monday as a result of easterly trades.
A small, long-period west swell originating from Typhoon Choi-wan also reaches the islands Thursday into the weekend, which may produce moderate surf for west-facing shores of the Big Island.
Small Craft Advisory until 6 PM HST Monday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.
