Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs around 85 near the shore to around 73 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows 68 to 73 near the shore to around 59 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 73 above 3000 feet. Southeast winds around 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 82. Southeast winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 72. East winds around 10 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82. Southeast winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 72 to 79 in the valleys to around 63 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 65 in the valleys to around 53 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 72 to 79 in the valleys to around 63 above 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 85. Southeast winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 72. Southeast winds up to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 75 to 85. Southeast winds around 10 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 75 to 84. South winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 73. East winds up to 10 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 84. Southeast winds around 10 mph. Chance of rain 50 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.

Data Courtesy of NOAA.gov