West Side

Today: Sunny. Isolated showers in the afternoon. Highs 77 to 85. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 64 to 73. Northeast winds up to 15 mph.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs 78 to 86. North winds up to 15 mph. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 85. North winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Clear. Lows 65 to 76. Northeast winds 10 to 15 mph.

Monday: Sunny. Isolated showers in the afternoon. Highs around 87. North winds 10 to 15 mph. Chance of rain 20 percent.

North Shore

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 81 near the shore to around 63 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to around 49 near 5000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 81 near the shore to around 65 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Central Maui

Today: Mostly sunny with isolated showers. Highs 79 to 85. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 67 to 72. Northeast winds 10 to 15 mph.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 87. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 60 at the visitor center to around 70 at the summit. Light winds. Chance of rain 40 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 44 at the visitor center to around 49 at the summit. Southwest winds up to 10 mph. Chance of rain 20 percent.

Monday: Sunny. Isolated showers in the afternoon. Highs around 62 at the visitor center to around 69 at the summit. Southwest winds up to 15 mph. Chance of rain 20 percent.

East Maui

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 81 near the shore to around 63 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to around 49 near 5000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 81 near the shore to around 65 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Lanai City

Today: Sunny. Highs 71 to 80. Northeast winds 10 to 15 mph decreasing to up to 15 mph in the afternoon.

Tonight: Clear. Lows 60 to 66. Northeast winds up to 15 mph in the evening becoming light.

Monday: Sunny. Isolated showers in the afternoon. Highs 71 to 80. Light winds. Chance of rain 20 percent.

Kaunakakai

Today: Sunny and breezy. Highs 68 to 87. Northeast winds up to 20 mph.

Tonight: Mostly clear. Breezy. Lows 56 to 75. Northeast winds up to 20 mph.

Monday: Sunny. Isolated showers in the afternoon. Highs 69 to 88. Northeast winds up to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Northeasterly trade winds should gradually weaken Sunday into Monday. Brief passing showers will drift into the islands on the trade winds, favoring windward and mountain areas during the overnight to early morning hours. A significant change to our weather pattern is expected early next week. Deep tropical moisture will bring the potential for heavy rain and thunderstorms across the state starting Monday night and persisting through at least Thursday.

Discussion

Radar this morning shows scattered showers along windward and mauka locations. Satellite imagery shows a large closed low about 900 miles to our northeast, a ridge to our northwest and another to our east-southeast. At the surface, a low is centered beneath the upper level low, with a ridge to either side.
Monday afternoon the low to our north will drift slowly southeast, both aloft and at the surface. At the same time, a low, CP94 and a new surface low will form to our west- southwest. A trough will connect these lows…the one that drifted into a position to our northeast along with the two to our west- southwest. Southerly winds will bring deep tropical moisture northward as this trough moves north toward and then through the state Monday night through Thursday. PWATs will get up over 2 inches, and max out around 2.5 inches.
Heavy rain and thunderstorms will be possible through this period over most of the state, but models are slow to converge on areas of maximum concern. A Hydrologic Statement describing the concern for flooding was issued yesterday afternoon. A Flood Watch may be issued if models continue to show the potential for heavy rain. Upper level winds may be just strong enough to enable the development of organized convection.
Winds will remain generally easterly through Tuesday, but after that there is uncertainty. Some models show centers of low pressure forming along the trough as it moves over the state. The location and timing of these lows depicted by various models, are quite different and therefore may result in wind variations in both speed and direction by island. This makes for a very low- confidence wind forecast. Regardless of exact timing/location of any additional lows that may form, it does not appear that strong winds will impact the state with this overall system. However, showers and any thunderstorms will have the potential for brief gusty winds.

Aviation

Moderate trades through the period. Low cigs and SHRA should primarily impact windward and mauka locations with limited spillover into leeward areas. MVFR conds possible in SHRA otherwise VFR prevails.
AIRMET Sierra is in effect for mtn obsc for Oahu to the Big Island. Conds should improve in the mid morning hours.

Marine

A surface low far northeast of the Hawaiian Islands will continue to dig southward today and stall roughly 800 nm northeast of the state by Monday, keeping the subtropical ridge just north of the area rather weak. In response, trade winds will remain gentle to moderate today, then decrease further to gentle by Monday. A low pressure trough will then approach the area from the southwest late Monday and bring heavy showers with embedded thunderstorms to the waters through much of the work week. Winds will remain in the gentle to locally moderate range.
A medium period north-northwest swell will slowly ease through Monday, with surf reaching near or slightly above seasonal averages. By late Monday, a long- period northwest swell will arrive and help generate moderate surf along north- and west- facing shores through Wednesday. A small north- northeast swell should arrive during the second half of this week.
A series of small overlapping south-southwest swells will keep surf along south-facing shores to around seasonal averages through early this week. A larger south-southwest swell may push surf slightly above seasonal average by mid to late this week.
Surf along most east-facing shores will be small through early next week, but areas exposed to wrapping northerly swells will experience periods of moderate surf through Monday. East-facing shores should also see a bump in surf if the north-northeast swell materializes during the latter half of this week.

Fire weather

Moderate trade winds with mostly dry conditions over leeward areas will continue to produce low to moderate fire weather conditions today. Ample tropical moisture will move in from the southwest beginning Monday night, bringing a threat for heavy rain through at least Thursday. As a result, fire weather concerns will be low through most of next week. Inversion heights will range from 6000-8500 feet.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov