An upper level trough passing through the Hawaii region today will keep high and middle level clouds over the islands with scattered showers and chances for a few thunderstorms mainly over the western islands. A series of low pressure systems developing northwest to north of the islands for the first half of this week will weaken the ridge north of the state, producing weak southeasterly wind flow lasting through Wednesday. The ridge builds back in north of the state by Thursday, allowing moderate easterly trade winds with passing windward showers to return lasting through the upcoming weekend.
Looking into the infrared satellite imagery this morning we see a Mesoscale Convective System with moderate to heavy showers and thunderstorms collapsing as scattered thunderstorms riding in on an outflow boundary fades as it approaches the western coastal waters of Kauai. A few of these thunderstorms will likely reach these western coastal waters early this morning, however the entire system will likely collapse into a more moderate rain band by the time it reaches the islands of Kauai and Niihau around sunrise. Elsewhere the passing upper level trough shown on satellite water vapor imagery will increase shower trends today across the state, especially along southeastern slopes of Haleakala on Maui and the southeast slopes of Mauna Loa on the Big Island this afternoon. Rainfall and thunderstorm coverage in the next 24 hours of the statewide forecast was adjusted upward to account for these smaller scale weather impacts.
An upper level trough will swiftly pass from west to east across the state today in southeasterly wind flow briefly enhancing shower activity as it passes over the island chain. An upper level ridge will build in behind the trough as the trough moves away from the islands from tonight into Tuesday. Expect drying trends as the upper level ridge builds stabilizing subsidence, downward moving warming and drying air, strengthening and lowering the subsidence inversion heights across the Hawaii region.
Stronger subsidence will build the surface ridge north of the islands, allowing trade winds to return to the region from Wednesday night on into the upcoming weekend. Subsidence inversion heights will range from 5,000 to 7,000 feet during this time period, high enough for brief passing showers favoring the typical windward and mountain areas in the overnight to early morning hours into Sunday.
Light easterly winds persist over windward aspects of the state today among some light and variable winds associated with land-sea breezes over leeward and interior regions. Winds will begin to veer more ESE late this afternoon into the evening hours. Light showers remain possible across windward and mauka areas, as well as over island interiors during afternoon hours. As the upper- level disturbance and associated surface trough approach the Hawaiian Islands from the west, expect cloud and shower coverage to increase statewide, with low-MVFR/IFR conditions possible within heavy, isolated showers. Otherwise, VFR conditions prevail.
No AIRMETs are currently in effect.
A trough of low pressure passing northwest of the state will act to weaken and veer winds east-southeasterly through mid-week across the local waters. Light wind flow should allow for afternoon sea breeze development near the shores. Isolated thunderstorms are expected to continue over the northwestern waters in the vicinity of the trough through tonight. By Thursday, high pressure ridging builds back in north of the state with fresh northeasterly trade winds returning to the region into next weekend.
Swell and surf will remain small along all shores through late today.
A small, medium-period northwest swell arrives tonight, bringing an uptick in surf along north and west facing shores for Tuesday before peaking on Wednesday. A moderate, medium- period north- northeast swell arrives on Tuesday and peaks also on Wednesday, bringing moderate surf to north and northeast facing shores, before slowly declining through the end of the week.
Another small, long-period west-northwest swell will enter the waters Wednesday night and provide a slight bump up for surf along west and northwest facing shores. Surf will continue to be small along south facing shores through the period. East facing shores will see an increase in surf with the arrival of the aforementioned north-northeasterly swell despite below-seasonal average trades.
None.
