West Side

Today: Mostly sunny. Windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 85. East winds 15 to 30 mph with gusts to 50 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Windy. Scattered showers in the evening, then isolated showers after midnight. Lows 69 to 75. East winds 10 to 30 mph. Chance of rain 40 percent.

Monday: Mostly sunny. Breezy. Scattered showers in the morning. Highs 75 to 86. East winds up to 20 mph. Chance of rain 40 percent.

South Side

Today: Mostly sunny. Breezy. Highs 76 to 87. Northeast winds 10 to 25 mph.

Tonight: Mostly clear. Breezy. Lows 68 to 73. Northeast winds 10 to 25 mph decreasing to 10 to 15 mph after midnight.

Monday: Mostly sunny. Highs 76 to 88. East winds up to 10 mph.

North Shore

Today: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 77 to 82 near the shore to around 65 near 5000 feet. East winds 10 to 25 mph. Chance of rain 80 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 67 to 74 near the shore to around 56 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 78 to 83 near the shore to around 68 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Central Maui

Today: Partly sunny in the morning then becoming mostly sunny. Windy. Isolated showers. Highs 80 to 86. East winds 10 to 30 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 68 to 74. East winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain 40 percent.

Monday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 81 to 86. East winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs 53 to 69. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 49 at the visitor center to around 47 at the summit. East winds 10 to 25 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly sunny with scattered showers. Highs 65 to 71. East winds 10 to 25 mph. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 77 to 82 near the shore to around 65 near 5000 feet. East winds 10 to 25 mph. Chance of rain 80 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 67 to 74 near the shore to around 56 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 78 to 83 near the shore to around 68 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Lanai City

Today: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 70 to 80. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Breezy. Lows 64 to 70. Northeast winds 10 to 20 mph decreasing to up to 15 mph after midnight.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs around 78. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny in the morning then becoming partly sunny. Windy. Isolated showers. Highs 67 to 85. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Tonight: Windy. Partly cloudy with isolated showers. Lows 59 to 76. East winds up to 30 mph decreasing to up to 20 mph after midnight. Chance of rain 20 percent.

Monday: Mostly sunny. Breezy. Isolated showers in the morning. Highs 76 to 87. East winds 10 to 25 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A strong high pressure system will build north of the Hawaiian Islands today on a slow eastward drift. Strong gusty winds will develop over and down stream of island mountain ranges today. Wind speeds will exceed advisory thresholds in the windier areas of all islands except for Kauai and Niihau. Passing showers are possible over windward and mountain areas through much of this week, higher rainfall amounts will favor the overnight to early morning hours.

Discussion

A combination of satellite and radar imagery shows unsettled 'open cell' cumulus clouds riding in on the trade winds producing periods of rain showers across much of the state. Higher rainfall amounts will favor windward mountain areas of all islands, especially in the overnight to early morning hours. Upper air weather balloon soundings from Lihue and Hilo at 2 AM HST (12Z) observed subsidence temperature inversion heights around 6,000 feet, high enough for periods of passing showers to remain in the forecast. Stronger low level winds will also help to lift unstable clouds up over island mountains orographically forcing enhanced rainfall activity.
A satellite scatterometry pass from last night around 9:40 PM HST, measuring wind speeds through microwave scattering of wind blowing over the ocean water, reported near Gale Force winds in the Kaiwi and Alenuihaha channels last night. This satellite wind report and our forecast for increasing winds through the day led to issuing Gale Warnings for the windiest channels and Wind Advisories through 6 PM HST for windier land areas over the down wind of island mountain ranges from Oahu eastward to the Big Island of Hawaii. Kauai and Niihau will likely remain just below our Wind Advisory thresholds today.
Enhanced showers will likely continue through much of this week. Initially, we see a low level cloud band moving across the islands from the north from Monday afternoon into Tuesday. Then a passing weak upper low tracks from west to east across the islands on Wednesday and Thursday lifting cloud heights, and finally we see yet another low level cloud band riding into the islands on the trade winds by Friday. In essence, these passing weather systems will keep periods of enhanced showers in the forecast into next weekend. Light to moderate beneficial rainfall amounts are expected in this weeks wet trade wind weather pattern.

Aviation

Breezy trade winds will continue today with brief periods of showers over windward and mountain areas, spilling into leeward areas at times. Localized afternoon sea breezes along leeward Big Island will lead to scattered showers developing along the Kona slopes. Brief periods of MVFR conditions may accompany some of the more robust activity.
AIRMET Sierra has been cancelled due to the improvement of ceilings and visibility.
AIRMET Tango remains in effect for low level moderate turbulence over and downwind of island mountains.

Marine

Strong trade winds expected today as a strong high builds far north of the islands. Some zones have been upgraded to a Gale Warning today, with the remaining coastal waters in the Small Craft Advisory (SCA). Winds will diminish gradually tonight and Monday as the high moves to the northeast, but a new north swell will push combined seas above 10 feet for exposed waters, likely prompting an extension of the SCA for most zones. Expect moderate to locally strong trade winds to require a SCA for the typically windy waters Tuesday through the remainder of the week.
A moderate, long-period north swell will build today and produce surf near High Surf Advisory thresholds along north-facing shores, as well as some exposed eastern shores into Monday morning. The north swell will gradually decline late Monday through Wednesday. A tiny pulse of northwest swell will be possible late next week, followed a moderate swell next weekend.
Rough surf along east-facing shores will remain above seasonal average over the next couple of days due to elevated trade wind swell and some wrapping north swell. East shore surf is expected to be around seasonal average Tuesday through the rest of the week. Mainly small background level surf will persist along south- facing shores through much of the week, though a small long- period swell will be possible on Friday.

Fire weather

Strong winds will develop today for most higher elevation mountain areas. Relative humidity levels in these areas will remain above critical fire weather thresholds. Wet weather conditions will also help to mitigate fire threats by increasing humidity levels in lower elevation areas. Temperature inversion heights near Maui and the Big Island will range from 6,500 to 7,500 feet elevation today.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST this evening for portions of Oahu, Molokai, Lanai, Kahoolawe, Maui and the Big Island of Hawaii.
Small Craft Advisory until 6 AM HST Monday for all Hawaiian coastal waters and channels outside of the Gale Warning area.
Gale Warning from 6 AM this morning to 6 PM HST this evening for Kaiwi Channel, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory from 6 PM this evening to 6 AM HST Monday for Kaiwi Channel, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov