West Side

Today: Partly sunny with scattered showers. Highs around 75. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 62 to 68. Light winds. Chance of rain 20 percent.

Monday: Partly sunny. Scattered showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs 71 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

South Side

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 79. Light winds. Chance of rain 30 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 61 to 70. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 78. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

North Shore

Today: Partly sunny. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 77 near the shore to around 61 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows around 65 near the shore to around 46 near 5000 feet. Light winds. Chance of rain 50 percent.

Monday: Cloudy. Occasional showers and isolated thunderstorms in the morning, then showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs around 74 near the shore to around 59 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

Central Maui

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 78. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 61 to 66. Light winds. Chance of rain 20 percent.

Monday: Partly sunny with scattered showers and isolated thunderstorms. Highs 73 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Upcountry

Today: Partly sunny. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 56 at the visitor center to around 59 at the summit. West winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 42 at the visitor center to around 36 at the summit. Southwest winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 20 percent.

Monday: Partly sunny with scattered showers and isolated thunderstorms. Highs around 54 at the visitor center to around 57 at the summit. Light winds. Chance of rain 50 percent.

East Maui

Today: Partly sunny. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 77 near the shore to around 61 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows around 65 near the shore to around 46 near 5000 feet. Light winds. Chance of rain 50 percent.

Monday: Cloudy. Occasional showers and isolated thunderstorms in the morning, then showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs around 74 near the shore to around 59 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

Lanai City

Today: Partly sunny with scattered showers. Highs 67 to 74. West winds up to 10 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 58 to 63. Northwest winds around 10 mph shifting to the northeast after midnight. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 65 to 73. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Kaunakakai

Today: Partly sunny with scattered showers. Highs 64 to 80. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 53 to 68. Light winds becoming northeast around 10 mph after midnight. Chance of rain 40 percent.

Monday: Mostly sunny with scattered showers in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Highs 62 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An upper level trough anchored over the islands will maintain relatively high chances for periods of return light to moderate shower activity. Weather conditions will improve through the morning, but widely scattered showers will persist through the day. Energy behind a boundary moving across the islands from the north later tonight into Monday morning will increase the probabilities for return moderate to locally heavy precipitation. The upper trough is forecast to lift northeast Tuesday. This will allow for drier mid week to commence under light to breezy trades.

Discussion

Drier weather is expected through this afternoon as a drier southerly air mass cyclonically rotates in across the island chain. There is still enough resident moisture and lingering instability in association with a diffuse mid to upper trough over the state to produce scattered showers that will primarily be focused along windward-facing slopes and upper terrain. Breaks in the mid to late morning overcast should allow the local developing sea breezes to better take hold. This will enhance interior cloud cover and assist in enhancing afternoon shower development. The overall weather pattern will undergo change tonight into early Monday.
Water vapor and IR satellite channels are depicting the next impetus to possibly more active weather late tonight into early Monday…that being a boundary moving south of 30N. This feature will help produce a large scale shearing pattern as strengthening north northeast winds over the western end of the state encounter more westerly downstream winds across the central and eastern end of the state. A deepening moist boundary layer to around 10k ft will keep any weak inversion layer high enough to promote more efficient precipitation processes. Moderate northeast winds in interaction with weakened downstream west to variable lower level flow will provide the lower to middle layer convergence needed to regenerate more frequent moderate to locally heavy rain episodes. Higher rain amounts will again become more rooted with the higher elevations and cells training in from the east southeast will again increase the late Sunday into early Monday flooding threat. A statewide Flood Watch may be required later today to account for this returning rain on top of already super saturated soils. Wet trade wind weather is expected through late Monday. An upper level ridge should begin to build over the region during the middle of the week and this should afford the islands a few days of drier weather.
The pressure gradient downstream of this approaching boundary has strengthened Mauna Kea and Mauna Loa winds enough to prompt a High Wind Warning for Big Island summits through this afternoon. The Winter Weather Advisory has been extended for Big Island summits through this morning as a wintry mix of light snow and freezing rain/fog persists through late morning.

Aviation

A trough just north of the islands will keep winds light and variable today, with sea breezes developing in most areas. Showers and thunderstorms will favor areas near the coast through the morning hours, then transition over to interior areas this afternoon. High pressure building to the distant north, will then push the trough back southward through the state tonight and Monday, bringing another round of heavy showers and a few thunderstorms and a return of breezy and gusty trade winds. Predominantly VFR conditions will prevail at most of the TAF sites today, with brief reductions to cig/vsby possible in showers and thunderstorms. MVFR cigs/vsbys will become more common tonight as the trough and associated heavy showers return to the islands.
AIRMET Sierra remains in effect for mountain obscuration on the Big Island. Conditions should improve here later this morning.
AIRMET Tango remains in effect for moderate upper level turbulence across the entire state. These conditions are expected to remain in place through the day.
AIRMET Zulu continues to mention light icing from 12 kft to FL240 across the entire state. Conditions are expected to improve later this morning.

Marine

A strong high pressure system building far north of the Hawaiian Islands continues to push a low level trough towards the state. This trough will continue to block large scale trade winds today with light and variable winds for all waters. Land and sea breezes expected for near shore waters of all islands. The low level trough will move into the islands from the north tonight through Monday. Fresh to strong trade winds and moderate to heavy rain showers and isolated thunderstorms will blow in across the region. Trade winds weaken again and veer more southeasterly from Thursday into Friday as another cold front approaches the island chain from the west.
Surf along exposed north and east facing shores will quickly build through the day Monday as a long period north-northeast (010-020 degree)swell from a broad storm force low develops off the northwest Pacific coast this weekend. A large area of northerly gales between this system and a 1040 MB blocking high will continue to drift southward. Surf heights will exceed advisory levels by Monday afternoon, possibly reaching low end warning levels by Monday night, for exposed north and east facing shores lasting through Tuesday. Although a gradual downward trend is anticipated by Wednesday, additional pulses from this same system will keep surf above advisory levels along east facing shores through much of the week. This swell direction will bring surf into some typically protected areas such as Kua Bay, West Maui, and exposed shores of Lanai.
Other impacts from this north-northeast swell direction will include overwash along vulnerable sections of coastline and roadways by Monday night during the early morning high tide cycles. Mariners can also anticipate harbor surges at Kahului and Hilo.
Surf along exposed west facing shores will rise early next week as a long-period northwest swell arrives from a recent broad storm force low over the far northwest Pacific. This swell will slowly fade into Wednesday.

HFO Watches/Warnings/Advisories

High Wind Warning until 6 PM HST this evening for Big Island Summits.
Winter Weather Advisory until noon HST today for Big Island Summits.

Data Courtesy of NOAA.gov