West Side

Today: Partly sunny with scattered showers. Highs around 81. South winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Lows 68 to 75. South winds 10 to 15 mph. Chance of rain 30 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 80. South winds 10 to 20 mph. Chance of rain 30 percent.

South Side

Today: Mostly sunny with isolated showers. Highs around 85. Southwest winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 67 to 76. Southwest winds around 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs around 85. Southwest winds 10 to 15 mph. Chance of rain 20 percent.

North Shore

Today: Mostly sunny with isolated showers. Highs around 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 70 near the shore to around 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the morning. Highs around 83 near the shore to around 67 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 20 percent.

Central Maui

Today: Mostly sunny with isolated showers. Highs 82 to 87. South winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 72. South winds around 10 mph. Chance of rain 20 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs 81 to 86. South winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Partly sunny with scattered showers. Highs around 62 at the visitor center to around 67 at the summit. Southwest winds up to 10 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows around 47 at the visitor center to around 45 at the summit. South winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning. Highs around 62 at the visitor center to around 67 at the summit. Southwest winds up to 15 mph. Chance of rain 20 percent.

East Maui

Today: Mostly sunny with isolated showers. Highs around 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 70 near the shore to around 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the morning. Highs around 83 near the shore to around 67 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 20 percent.

Lanai City

Today: Partly sunny with scattered showers. Highs 72 to 79. South winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 67. South winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 71 to 79. South winds 15 to 20 mph. Chance of rain 30 percent.

Kaunakakai

Today: Partly sunny with scattered showers. Highs 70 to 86. South winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 74. South winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 40 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 70 to 85. South winds 10 to 20 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

An approaching cold front from the northwest will weaken into a trough as it reaches the far west nearshore waters this evening. This dying front will merge with what is left of an old convergence boundary. The bonding of these two features will provide better focus for redeveloping and lingering mid to late week rain episodes and isolated thunderstorms that will primarily impact Niihau, Kauai and Oahu. High pressure will begin to take hold over the state at all levels this weekend and translate to a drier pattern heading into the holiday week. Trades will return over the weekend and significantly strengthen to breezy to locally strong magnitudes early next week.

Discussion

The remnants of a trough, now a lower level convergent zone over the western half of the state, that provided a pathway for more moisture-rich southerly air to move in and assist in producing subsequent Kauai and Oahu rain the past couple of days, is giving way to a surface ridge axis from the northeast. Kauai and Niihau picked up another few tenths to nearly two inches of precipitation overnight with Oahu's upper terrain capturing a few tenths of an inch of rain from quick hitting showers traveling up within the southerly flow. Today will be a similar day for both Honolulu and Kauai Counties compared to Monday's rain behavior with occasional showers putting down an additional few hundredths to a tenth or an inch along their northern route. The next rain maker will be from a weakening front moving in from the northwest today and stalling in the vicinity of Kauai County later this afternoon into evening.
There will not be much upper level support to push tonight into Wednesday morning's boundary eastward. As the associated upper lower low near 27N170W ejects northeastward up and over upper ridging anchored over the eastern Pacific it will take much of the energy that will be required to push the low level boundary eastward. Shortwave energy passing around the base of the trough Wednesday may be the impetus to advancing the trough/convergence zone further east toward Oahu. Thus, confidence is low that that this latest trough will make it much past Kauai. As was the case the past couple of days, the stretched lower to middle level frontal zone will provide a channel for higher moisture to ride up from more southern latitudes. The southern branch of the polar jet nosing in from the west at mid week may provide enough downstream difluence, along with any shortwave riding up from the southwest, to trigger periods of numerous showers and that rouge thunderstorm. Since most of the island chain will be shrouded with mid to high level clouds the next few days, the lack of sun will cross off any convective surface initiation. Future rain production will be from upper level forcing within an ongoing moisture rich air mass residing over the state. Periodic oceanic clustering rain cells may become organized enough to quickly lay down 1 to 2 inches. This may create mid week nuisance flooding and the ponding of water within low lying areas over the western islands of Oahu and Kauai. Maui and Hawaii Counties will also receive rain but it will be much more limited as showers will be surface-based convection from lift created by the local diurnal breezes.
Showers will linger on through Friday but a drier trend will commence around Friday when the lower level southerly flow begins to back more easterly. Trades attempt a comeback Friday but will be in full force by Saturday. Upper ridging will form over the islands and this subsidence will kick off several days of typical trade weather in the days leading up to Christmas. Model guidance is suggesting that a large and in charge North Pacific surface high (around 1045 mb) will press down a tight enough pressure gradient to significantly strengthen trades this time next week. If this scenario comes to fruition, expect moderate to locally strong-in-gust easterlies from Monday through Wednesday.

Aviation

A surface trough will linger northwest of Kauai enhancing showers and producing isolated thunderstorms along the trough axis. Southerly winds across the state will produce unsettled weather conditions with brief MVFR conditions in low clouds and showers across the islands of Kauai, Oahu, Molokai, and Lanai today. The eastern islands of Maui and the Big Island will remain more stable with prevailing VFR conditions for most airfields. Southerly winds may bring daytime wind gusts in the 20 to 25 kt range over northern slopes of island mountains.
AIRMET Sierra remains in effect for tempo mountain obscurations for Oahu, Molokai and Lanai this morning. These low cloud ceilings should improve by the afternoon hours.
AIRMET Tango for tempo moderate turbulence aloft FL240 to FL340 above Kauai and Oahu associated with the subtropical jet stream over the islands.

Marine

Weak surface trough is near Kauai and another cold front is immediately west of the islands this morning. This front maintains a chance for isolated thunderstorms over the western nearshore waters through at least Wednesday. Locally fresh S to SW winds emerge in the meantime as the low digs south of 30N. Winds then weaken late this week followed by returning trades perhaps as early as Sunday.
A long period N swell has peaked overnight and will continue to drop through today. The High Surf Advisory (HSA) will be allowed to expire at 6am. The Small Craft Advisory will also expire at 6am as seas drop below criteria. Renewed energy out of the NW quadrant (300-320) will elevate surf near the HSA threshold once again early Wednesday through Thursday.
E shores remain flat except where long period NW-N swell energy wraps. S shores experience short period wind wave chop and S fresh swell energy due to persistent S-SW winds through the week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov