Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 84 near the shore to around 73 above 3000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 66 to 71 near the shore to around 59 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 83 near the shore to around 71 above 3000 feet. North winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

South Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 79 to 86. Southwest winds up to 10 mph shifting to the south in the afternoon. Chance of rain 40 percent.

Tonight: Cloudy with scattered showers. Lows around 70. West winds around 10 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 77 to 84. West winds around 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly sunny early in the morning, then isolated showers late in the morning. Partly sunny with scattered showers in the afternoon. Highs 74 to 82 in the valleys to around 65 above 4000 feet. Southwest winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 68 in the valleys to around 57 above 4000 feet. Southwest winds up to 15 mph. Chance of rain 60 percent.

Thursday: Numerous showers in the morning, then frequent showers and isolated thunderstorms in the afternoon. Highs 70 to 79 in the valleys to around 62 above 4000 feet. Light winds becoming north up to 15 mph in the afternoon. Chance of rain near 100 percent.

North Kaua’i

Today: Mostly sunny. Isolated showers in the late morning and afternoon. Highs 75 to 85. South winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 62 to 70. South winds up to 15 mph. Chance of rain 50 percent.

Thursday: Scattered showers in the morning, then frequent showers and isolated thunderstorms in the afternoon. Highs 73 to 83. South winds up to 10 mph shifting to the north in the afternoon. Chance of rain near 100 percent.

East Kaua’i

Today: Mostly sunny early in the morning, then isolated showers late in the morning. Partly sunny with scattered showers in the afternoon. Highs 74 to 85. Southwest winds up to 15 mph shifting to the south in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 74. Southwest winds up to 15 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy. Scattered showers in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 70 to 83. West winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Increasing southerly winds and moisture ahead of an approaching cold front and upper disturbance will lead to better rainfall chances for portions of the state later today through the second half of the week. The front will reach Kauai on Thursday, then stall and begin to diminish over or around Oahu Thursday night into Friday. Breezy north-northeast winds will fill in behind it Thursday and Thursday night over the western end of the state, with a brief return of trades Friday. A second front passing north of the area over the weekend could lead to the trades weakening again.

Discussion

A transition period is anticipated today through tonight as upper heights begin to lower in response to a shortwave trough digging southward into the area. Increasing southerly winds and lift ahead of the attendant cold front could lead to a few pre-frontal showers today, especially through the late morning and afternoon hours for the western end of the state. Early morning radar and satellite data reflect this potential with a few light showers developing over the waters south of Oahu and Kauai, and along the southeast Big Island coast. The better dynamics (35 to 45 kt 0-6 km shear) and upper height falls are expected tonight over and around Kauai as the front draws closer. Although the chances are low, a thunderstorm or two can't be completely ruled out, especially over the adjacent waters north of Kauai tonight and into Thursday.
The front will stall and slowly diminish around Oahu Thursday night through Friday as the shortwave trough begins to lift northeastward and away from the area. Breezy north to north- northeast winds trailing the front Thursday and Thursday night over the western end of the state will veer out of the east on Friday, with the residual moisture associated with the front retreating westward. A brief return of light trade winds is possible over the weekend as another front passes to the north.

Aviation

Stable conds expected through the first half of today. The second half of today through Friday a front approaches the islands. Winds should become light to moderate with frontal approach. This should also increase the chances for some SHRA and low cigs. MVFR conds can be expected in any SHRA, however VFR should prevail.
No AIRMETs in effect.
AMD NOT SKED in at PHJR and PHMK for equipment issues, with no estimated time for repair.

Marine

An E-W oriented surface ridge extending over the islands from the E is supporting gentle winds statewide that are out of the E-SE over Big Island waters, and from the S-SW over Kauai and Oahu waters. Little overall change in the ridge's position is expected today. A low passing N of the islands late tonight and Thursday will force the ridge eastward, with a tightening low-level gradient supporting fresh to locally strong S to SW winds near Kauai and Oahu as a front approaches from the NW. Fairly high confidence in the front moving over Kauai on Thursday, then stalling near Oahu from late Thursday into Friday. Winds and/or seas will likely reach Small Craft Advisory (SCA) criteria in at least some of the waters Thursday and Friday, and the front will bring a slight chance of thunderstorms.
As the front stalls and dissipates, locally fresh to strong post- frontal N winds over Kauai and Oahu will gradually ease and veer to the NE Thursday night into Friday, while light to moderate E winds will prevail over Maui and Big Island waters. Wind speeds will quickly diminish statewide on Saturday, then light to moderate ENE trade winds on Sunday are expected to strengthen next week as high pressure builds to the distant NE.
Long fetches of near-gale to gale-force winds associated with low pressure systems passing well N of the area will send NW swell of varying sizes and periods toward the islands the next several days. Most of the swell energy will be in the shorter- period 12-14 second bands, with resultant surf expected to be near or above High Surf Advisory (HSA) levels along exposed N and W facing shores into the weekend.
In the short term, swell heights at NDBC buoys 51001/51101 NW of Kauai have diminished slightly overnight, with a primary period ~12 seconds. The High Surf Advisory (HSA) for exposed N and W facing shores has been cancelled. Another NW swell late Thursday into Friday will likely produce HSA-level surf, with a smaller NNW pulse possible next weekend.
A long-period S swell is will gradually decline through Thursday. Another long-period S swell is expected by this weekend, but it will likely be a little smaller than this swell at its peak.

HFO Watches/Warnings/Advisories

None.

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