A cold front will approach from the northwest today, move through and produce some showers on Kauai and Oahu tonight, then stall out across the central islands late Wednesday through Thursday bringing some periods of showery weather. Some more unsettled weather is possible Friday through the weekend as a plume of deeper moisture develops along the front while a disturbance aloft moves across the state. Drier weather and improving conditions are then expected early next week as ridging builds across the island chain.
Currently at the surface, a cold front is located a few hundred miles west-northwest of Kauai, while a 1024 mb high is centered to the distant northeast. Infrared satellite imagery shows clear to partly cloudy skies across most of the state, with a few pockets of more extensive cloud cover. Radar imagery shows a few very light showers affecting windward slopes and coasts with dry conditions elsewhere. The main short term focus revolves around the incoming front.
The front will push steadily southeastward toward the islands today, with a few showers possibly developing in advance of the front late this afternoon over Kauai. Elsewhere, a few light showers may affect windward areas this morning, and develop over the island interiors this afternoon. A better shot for rain will move into Kauai tonight as the front moves through, bringing some breezy northerly winds in its wake. The progressiveness of the front should slow considerably tonight as the mid-level flow becomes parallel to the feature, although an increase in showers should occur over Oahu after midnight as the decaying front moves in.
The front is forecast to stall out in the vicinity of the central islands late Wednesday through Thursday. Model guidance is in fairly good agreement showing a shortwave trough moving overhead Wednesday night and Thursday, which could enhance some showers particularly across windward sections of Oahu and Maui County. Late in the week and over the weekend, the model solutions, their ensembles, as well as the AI versions of both the GFS and ECMWF suggest some more uncertainty in the forecast. Overall, the pattern appears to favor a somewhat unsettled period as moisture pulls along the stalled out frontal boundary and upper level troughing moves overhead. Improving conditions are then forecast for early next week as deep layer ridging builds over the island chain.
Light to moderate east-southeasterly in advance of a cold front will keep a land and sea breeze pattern in place today. The cold front will move through Kauai tonight, bringing breezy northerly winds in its wake. Mainly VFR conditions are expected during the next 24 hours, although some MVFR cigs/vsbys could affect Kauai by late this afternoon and Oahu overnight, particularly along north facing slopes and coasts.
No AIRMETs are currently in effect. AIRMET Tango may be required for moderate upper level turbulence later this morning due to jet stream winds. AIRMET Sierra may be needed for mountain obscuration for Kauai by late this afternoon.
A cold front approaching the area will reach Kauai late this evening, then Oahu early Wednesday, before stalling and weakening near Maui County by Thursday. Light to moderate south to southeast winds will shift to northerly and strengthen along and behind the front. This will prompt Small Craft Advisory conditions, particularly over the Kauai waters beginning tonight, and potentially around Oahu by Wednesday as the front progresses down the island chain. Seas will respond and become rough over these waters, potentially nearing or reaching advisory-level seas around 10 ft tonight into Wednesday. High pressure will build north of the state Thursday into Friday, followed by another frontal system evolving west of the state that may approach this weekend.
Surf along exposed north- and west-facing shores will remain small this morning as a medium-period north-northwest swell lingers. An upward trend is expected later today as a fresh, long- period west-northwest swell arrives and builds down the island chain. Offshore buoy observations reflect this trend, showing increasing energy in the 16 to 17 second bands. Strong northerly winds associated with the front, combined with near advisory- level surf, will result in rough conditions along exposed north- facing shores of Kauai and Oahu by tonight as this swell peaks. Elsewhere, surf is expected to remain below advisory levels. Overlapping pulses expected Wednesday and Thursday, similar in size, will support surf holding near advisory levels for exposed north- and west- facing shores, mainly on Kauai and Oahu, through the second half of the week. A downward trend is expected late Friday into the weekend, with mainly a small, long- period west- northwest swell anticipated.
Surf along east facing shores of Kauai and Oahu could rise tonight into Wednesday in response to the strong north-northeast winds accompanying the front. Otherwise, surf should remain below average this week due to the lack of fresh to strong trades locally and upstream.
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