West Side

Today: Mostly sunny with isolated showers. Highs 78 to 86. Northeast winds up to 10 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 61 to 70. Northeast winds up to 10 mph shifting to the south after midnight.

Tuesday: Mostly sunny. Isolated showers in the morning. Highs 78 to 86. East winds 10 to 15 mph. Chance of rain 20 percent.

South Side

Today: Sunny. Highs around 87. North winds up to 10 mph shifting to the southwest around 10 mph in the afternoon.

Tonight: Mostly clear. Lows 61 to 67. West winds up to 10 mph.

Tuesday: Sunny. Highs around 87. East winds 10 to 15 mph.

North Shore

Today: Breezy. Mostly sunny with scattered showers. Highs 78 to 83 near the shore to around 54 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 62 to 69 near the shore to around 48 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 78 to 83 near the shore to around 54 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Central Maui

Today: Sunny. Highs 83 to 88. North winds up to 10 mph shifting to the east in the afternoon.

Tonight: Clear in the evening, then partly cloudy with isolated showers after midnight. Lows 60 to 70. East winds around 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 83 to 88. East winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Sunny. Highs around 51 at the visitor center to around 46 at the summit. Light winds becoming east up to 10 mph in the afternoon.

Tonight: Mostly clear with scattered showers. Lows 42 to 53. East winds up to 10 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Sunny. Highs around 51 at the visitor center to around 46 at the summit. East winds 10 to 15 mph.

East Maui

Today: Breezy. Mostly sunny with scattered showers. Highs 78 to 83 near the shore to around 54 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 62 to 69 near the shore to around 48 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 78 to 83 near the shore to around 54 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Lanai City

Today: Mostly sunny with isolated showers. Highs 70 to 79. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 62. Northeast winds up to 10 mph shifting to the northwest around 10 mph after midnight. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the morning. Highs 69 to 78. East winds around 10 mph. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny. Isolated showers in the afternoon. Highs 73 to 83. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Scattered showers after midnight. Lows 61 to 69. East winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday: Mostly sunny. Isolated showers in the morning. Highs 74 to 84. East winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The high pressure ridge over the islands has diminished this morning as a surface low begins to develop just west to northwest of the state. Expect a stable light southerly wind pattern transitioning to east to southeast winds later today and tonight. A surface low will develop today, increasing east to southeast winds through Wednesday. Shower trends will gradually increase through the week in moderate to locally breezy east to southeast wind flow.

Discussion

The high pressure ridge over the islands has diminished this morning as a surface low begins to develop just west to northwest of the state. The weather pattern will change today as the surface ridge is gone and east to southeast winds will increase across the island chain. Satellite imagery this morning shows increasing shower activity along land breeze and island plume convergence zones mainly over the coastal waters. High level cirrus clouds continue to pass over the region due to a subtropical jet stream and an upper level trough stalling out farther to the northwest of the state. These high clouds will decrease surface heating over each island by a few degrees hindering convective showers. Island plume convergence zones will strengthen tonight with stronger diurnal boundary layer forcing.
The upper air balloon soundings from 2 AM HST at Lihue and Hilo show temperature inversion heights around 6,000 to 7,000 feet. These inversion heights will continue to limit cloud heights and shower potential through the overnight hours. Inversion heights will slowly rise through Wednesday, as the surface low deepens to the northwest and stronger winds blow across the region. Shower trends will gradually increase through the week in moderate to locally breezy east to southeast wind flow.
Global models remain fairly consistent that most of the heavier shower activity with this developing low will remain west of Kauai through the week. Chances for showers over the islands will depend upon small scale convergence band development, such as island plumes or wind speed convergence in a less stable environment. Brief periods of showers will favor the overnight to early morning hours as stronger winds return.

Aviation

A stationary front northwest of the Hawaiian islands will maintain southeast flow through today. Winds will gradually strengthen this afternoon and turn more easterly. A couple showers could drift over the islands today, then a slight increase in shower coverage is possible tonight. Overall VFR conditions are expected.

Marine

A surface boundary is stalling northwest of the islands with the pressure gradient north of this stationary front being tight enough to support gale force winds. Gales will primarily impact the far northwest offshore waters north of 24N through the day. Today's moderate winds across the nearshore waters will veer more southeasterly in response to the front. Low pressure will likely develop along the front today as surface high pressure to the north expands east of the islands through the middle of the week. This will tighten the pressure gradient east of the state and strengthen easterly trades Tuesday and Wednesday. A north swell moving through the Kauai waters today will lift seas to Small Craft Advisory (SCA) levels. A SCA is also in effect from tonight through the middle of the week for winds across eastern island windward waters including the notoriously windier areas surrounding Maui County and Big Island. As the weakening low lifts north and away from the area into the latter half of the week, moderate to locally fresh east to southeast winds will occur through Friday. The eastern Pacific pressure gradient is currently forecast to remain tight enough to maintain moderate to possibly locally strong trades into early next week.
A medium size, short period north (360-020 degree) swell generated by the winds behind a stalling front northwest of the islands is arriving this morning. This swell will produce small to moderate size surf along most smaller island north-facing shores through tonight and will gradually decline Tuesday. A mix of small north northwest swells may maintain modest surf along many exposed north and west-facing shorelines Wednesday into Friday. These north swells may wrap around and subtly increase surf along east-facing shores with more northern exposures through Tuesday. Strengthened mid week trades will result in more choppy wind waves along east-facing shores. A very small, long period south (190 degree) swell arriving today will result in an additional foot or two of surf along many south- facing shores through Tuesday before gradually lowering on Wednesday.

HFO Watches/Warnings/Advisories

Small Craft Advisory from 6 AM this morning to 6 PM HST this evening for waters around Kauai exposed to north swell.
Small Craft Advisory from 6 PM this evening to 6 PM HST Wednesday for most windier waters and channels around Maui and the Big Island.

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Data Courtesy of NOAA.gov