A high pressure system will linger north of the Hawaiian Islands producing moderate to breezy trades through the middle of next week with minor fluctuations in speed. Brief pulses of enhanced showers will roll through on the trades during this time period, with showers favoring windward mountain areas in the overnight to early morning hours.
This mornings satellite imagery shows the first of three easterly waves continues to slowly drift through the islands enhancing shower activity through the early morning hours. Two additional weak atmospheric waves will drift from east to west across the islands on Saturday evening, and from late Sunday into Monday. Cloud and shower coverage will increase with each passing wave, favoring the overnight to early morning hours with the highest rainfall amounts falling over the windward mountain areas of each island. A wet trade wind pattern for sure with pulses of showers affecting each island through Monday.
A brief drying trend will develop by Tuesday as the last of the easterly waves passes to the west of the state. Subsidence aloft will lower temperature inversion heights with more stable trends reducing clouds and shower activity lasting through Wednesday. Expect the typical brief passing showers during the overnight hours over the windward mountain areas.
The long range forecast remains fairly uncertain as global models continue to struggle in finding a consistent solution with a passing short wave mid latitude trough passing just north of the Hawaiian Islands. The model solutions have flipped over the past few days with the American (GFS) model now showing a drier high pressure ridge setting up north of the island chain, and the European (ECMWF) model showing a cold core low, cut off from the mid latitude westerly winds, deepening just north of the state. The ECMWF solution would bring southeasterly to southerly winds over the islands, drawing up unstable tropical moisture from the deep tropics and triggering a period of wet weather across the islands. While the American GFS model shows more typical easterly trade wind weather with brief passing shower activity. Unfortunately these large scale differences are impossible to blend and we will have to wait a bit longer for our global weather model solutions to converge on a more consistent solution. Stay tuned for changes to the long range forecast.
Moderate to breezy trades through the period. Low cigs and SHRA should impact windward and mauka locations with some limited spillover to leeward areas. MVFR conds possible in SHRA, otherwise VFR prevails.
AIRMET Sierra is in effect for mtn obsc for portions of all islands due to cld and SHRA. Conds should improve in the mid morning hours.
AIRMET Tango is in effect for mod turb lee of terrain. Expect this continue for a few days.
High pressure north of the islands maintains fresh to strong trades well into next week. The Small Craft Advisory (SCA) remains in effect for the typically windy waters around Maui County and the Big Island and has been expanded westward to the Kaiwi Channel beginning this morning. The SCA may need to be further expanded in areal coverage tonight as trades undergo modest strengthening.
A rather short period NNW swell peaked overnight in the 5 to 6 foot range and will bring seasonable surf to N shorelines. This swell will slowly decline and shift to the N during the weekend as a smaller overlapping NW swell moves through the area. Both swells lower on Monday and fade on Tuesday. Another small NW swell is possible next Thursday or Friday.
A declining small, medium period S swell will maintain below average surf along S shorelines through next week.
Surf along E shores increases this weekend as trades strengthen. In addition, expect some wrap of NNW swell for exposed shorelines through at least today. Rough trade wind swell will produce above average surf for E shores through Tuesday before declining with weakening trades mid-week.
Small Craft Advisory until 6 AM HST Monday for Kaiwi Channel- Maui County Leeward Waters-Maalaea Bay-Pailolo Channel- Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.
