Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Partly sunny with scattered showers. Highs around 91 near the shore to around 79 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 75 near the shore to around 65 above 3000 feet. Northeast winds around 10 mph. Chance of rain 50 percent.

Friday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 92 near the shore to around 79 above 3000 feet. Northeast winds up to 10 mph in the morning becoming light. Chance of rain 70 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 82 to 90. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly cloudy with numerous showers. Highs 84 to 92. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy with numerous showers. Highs 75 to 88 in the valleys to around 68 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 67 to 74 in the valleys to around 62 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with numerous showers. Highs 76 to 88 in the valleys to around 69 above 4000 feet. Northeast winds 10 to 15 mph decreasing to up to 10 mph in the afternoon. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 78 to 91. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 69 to 76. East winds around 10 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with numerous showers. Highs 77 to 92. Northeast winds around 10 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 87. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows 68 to 78. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with numerous showers. Highs 76 to 89. Northeast winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A surface ridge of high pressure far north of the Hawaiian Islands will maintain moderate to fresh trade winds through today, with periods of embedded showers moving into windward and mountain areas. Tropical storm Gilma is expected to weaken to a depression today and Tropical storm Hector has weakened to a remnant low. The main impacts from these weak systems as the pass near or over the state is enhanced rainfall that can begin as early as tonight and persist into the weekend.

Discussion

Moderate to locally fresh trade winds will continue through today as a broad ridge of high pressure remains centered far north of the state. A moisture plume extending well out ahead of Tropical Storm Gilma can be seen clearly on CIMSS MIMIC precipitable water satellite imagery. Radar and satellite imagery shows some moderate to locally heavy rainfall embedded in some scattered clouds mainly along windward and mauka areas with some showers making it over some leeward areas. A narrow swath of drier air and some weak subsidence ahead of Tropical Storm Gilma may briefly reduce the shower activity today. Even though slight subsidence is expected today, afternoon heating along the upper kona slopes of the Big Island may be enough to produce some thunderstorms so have added a slight chance for this area this afternoon.
Gilma is forecast to weaken to a tropical depression today and then a remnant low as it tracks northwest just east of the state late tonight. Current forecast trends have the strongest winds (around 30 kts or less) to remain over the eastern coastal/offshore waters. Winds along land areas and leeward coastal waters will actually weaken and take on a more southeasterly component Friday into Saturday. These weaker winds may allow for shower coverage to expand across leeward portions of the state due to increased potential for sea breeze activity and increased moisture being routed up the island terrain. Timing of the heaviest rainfall is looking like it will be Thursday night into Friday for the Big Island and Maui. As the remnants continue a northwest track, chances of heavy rainfall will then focus near Oahu and Kauai Friday night into Saturday. Current rainfall totals range between the 1 to 3 inches. Even though widespread flooding is not expected, localized flooding could be possible. Have also added isolated thunderstorms to the forecast during this time as the environment becomes increasingly unstable. Dewpoint temperatures are currently in the low 70s and will continue to rise to the mid 70s as the remnants of Gilma skirts just east of the state. This combination of high dewpoints and lighter winds will make the air feel warmer than usual.
With all of this said, slight variations in the track would bring noticeable differences in the forecast. A slight shift in forecast track to the north would mean less rainfall for the islands, and a slight shift to the south would bring higher rainfall totals across the state. Stay tuned for forecast updates.
Remnants of Tropical Storm Hector will follow closely behind Gilma as a weak surface trough with a diffuse moisture plume sometime Saturday night into Sunday. This will bring a slight uptick in shower activity during this period. Dewpoint temperatures will continue to fluctuate between the low to mid 70s. Moderate to locally fresh trades will gradually return, first for the eastern half of the state then to the western half of the state Sunday. No significant impacts are expected from remnants of Hector at this time.
Heading into next week, moderate to locally strong trades will return and dewpoints will dip down back down to more typical summertime averages as high pressure builds across the state, bringing drier air and limiting cloud and shower coverage.

Aviation

A broad high pressure ridge far north of the Hawaiian Islands will keep moderate to locally fresh trade winds blowing across the region today with weaker winds in the forecast for Friday as the weakening center of tropical cyclone Gilma passes just north of the island chain. Deeper moisture levels will enhance showers mainly over windward and mountain areas, favoring the overnight to early morning hours. Periods of MVFR conditions are expected mainly along windward and mountain slopes of each island in the overnight to early morning hours. Otherwise mostly VFR conditions will prevail.
Tropical Storm Gilma continues to weaken as it approaching the Hawaiian waters from the east. This system will be more of a low cloud and rain threat for aviation as it tracks just north of the Hawaiian Islands on Friday. Isolated thunderstorms are also possible mainly near the low center and over the Big Island.
AIRMET Sierra for tempo mountain obscuration remains in effect for the north and east sections of the Big Island, Maui, Molokai, Oahu and Kauai this morning. This AIRMET will likely continue through the early morning hours.

Marine

Moderate to locally fresh trade winds will remain today as Gilma approaches and weakens from the east. Currently, Gilma's center will enter the eastern offshore waters this morning and is forecasted to briefly disrupt the trade wind flow starting late tonight over the eastern coastal waters. Gilma is forecasted to move northwest over the windward waters of the islands through Friday night. In the wake of the tropical storm, winds veer to southeasterly with the strongest winds confined to the northern half the system. Relatively minimal change is anticipated in the magnitude of winds in the nearshore waters during this time. However, this will be sensitive to the exact track and will be subject to revision in future forecasts. Moderate to locally fresh east southeast winds will trend in the wake of Gilma on Saturday before high pressure to the northeast builds in as trade winds return through the early part of next week.
Surf along east facing shores will remain small to moderate as the medium period energy lingers today before slowly declining through the end of the week.
Surf along south facing shores will continue to trend down through the end of the week. The weekend may see tiny background southwest and southeast swell energy but will remain tiny to small. Summertime average surf may return next week as a series of small, long period southerly swells begin to fill.
North facing shores will see small surf develop late tonight into Friday as a small northwest, medium to long period swell fills in. This swell will peak Friday and gradually diminish through the weekend.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov