West Kaua’i

Today: Mostly cloudy with scattered showers and isolated thunderstorms. Highs around 89 near the shore to around 74 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Cloudy. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Lows around 73 near the shore to around 61 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly cloudy with scattered showers and isolated thunderstorms. Highs around 89 near the shore to around 74 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers in the afternoon. Highs 81 to 88. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy. Showers and isolated thunderstorms in the evening, then numerous showers and isolated thunderstorms after midnight. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Friday: Cloudy and breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 81 to 89. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Cloudy with numerous showers and isolated thunderstorms. Highs 74 to 86 in the valleys to around 65 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Showers and isolated thunderstorms. Lows 66 to 71 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain near 100 percent.

Friday: Cloudy with numerous showers and isolated thunderstorms. Highs 73 to 86 in the valleys to 62 to 67 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 79 to 88. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Lows 65 to 74. Southeast winds around 10 mph. Chance of rain 80 percent.

Friday: Cloudy with numerous showers and isolated thunderstorms. Highs 78 to 88. East winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 75 to 86. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Lows 66 to 77. Northeast winds up to 10 mph. Chance of rain 90 percent.

Friday: Cloudy with numerous showers and isolated thunderstorms. Highs 75 to 86. East winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

An unstable moderate to locally breezy trade wind weather pattern will continue into Saturday as an upper low near Kauai and Oahu and low level convergent cloud bands riding in on the easterly trade winds bring periods of showers to all islands. Some of these showers will be locally heavy at times with thunderstorms possible over the western half of the state through Saturday morning, and portions of the Big Island later today. Enhanced showers will linger into early next week as another upper low moves in from the north and settles in over the western half of the state.

Discussion

The satellite imagery this evening shows the upper level low center settling in over Kauai and Oahu. Deeper convection and showers are developing under this upper level disturbance. The heaviest showers last night appeared to pass just north of the smaller islands likely due to east-southeasterly steering winds at around 5,000 feet, causing the stronger showers to move parallel to the smaller islands. The north shore and east Maui observed up to a quarter inch of rainfall last night, and the north and eastern slopes of Kauai also received up to a half inch of rainfall in the stronger shower bands. Temperature inversion heights as measured by upper air balloon soundings from Lihue and Hilo at 2 AM HST (12Z) this morning were observed around the 7,000 to 8,000 foot range. Overall these higher inversion heights continue to support periods of wet weather for all islands.
These periods of enhanced showers are forecast continue into Saturday, with slightly decreasing trends into Sunday as the upper low drifts westward away from the islands. The forecast challenge today will be in forecasting the low level cloud steering wind directions. A more easterly direction will push these clouds directly into island mountains, producing higher rainfall totals. The steering winds last night from the east- southeast direction likely limited rainfall totals for the smaller islands as compared to our forecast. The latest short range model solutions show a more easterly direction on these low level steering winds later today into Friday as the upper low beings to drift westward, allowing higher pressure to build back into the region.
Another upper level low descends over the western islands on Monday, producing a very similar wet weather pattern over the islands through the first half of next week. Rainfall amounts for each island will heavily depend on smaller (mesoscale) convergent bands. Trade winds will lift unstable clouds over windward island mountain areas where the highest rainfall totals are favored. Western islands may see locally heavy rainfall and possible thunderstorms during this time period. Stay tuned for more weather details for early next week as this next system approaches the islands from the north.

Aviation

An upper level low centered near Kauai will drift slowly west southwest today and bring unsettled weather to all islands. Trade wind flow will bring bands of scattered to numerous showers over windward areas with slightly less coverage over leeward sides. Instability aloft should allow for isolated thunderstorm development over areas north and west of Oahu today with isolated thunderstorms possible over all of the smaller islands tonight. Isolated thunderstorms may also develop over leeward portions of the Big Island this afternoon due to diurnal heating. Heavier shower and storm activity will be capable of producing MVFR and isolated IFR ceilings and visibility.
AIRMET SIERRA for tempo mountain obscuration remains in effect for north thru east sections of Kauai, Maui, and the Big Island above 2000 feet due to low clouds and showers. SIERRA will likely continue through the remainder of today as the clouds continue to bank up along the windward sides of the island.
AIRMET TANGO remains in effect for Oahu, Molokai, Maui, and the Big Island for tempo moderate turbulence between FL220 and FL350. This is expected to continue through the day.

Marine

Moderate to locally strong trades winds have filled in across the Hawaiian coastal waters as a surface high strengthens far northeast of the state. A Small Craft Advisory (SCA) remains in effect for typical windy waters around Maui County and the Big Island through 6 PM HST Friday. The SCA will likely be extended into the weekend as another high quickly builds north of the state and tracks east. An upper low will drift from east to west across the state today into the weekend, keeping isolated thunderstorms over the forecast waters into the weekend.
A reinforcing moderate, long period northwest swell energy will fill in early this morning, maintaining near to above average surf along north and west facing shores through Friday. A brief moderate, long period NNW swell will move through Friday, but should taper off Saturday keeping surf elevated. Surf along north and west facing shores will trend down through the weekend. A hurricane force low is expected to develop east of Japan later today and could bring another round of moderate, long period northwest swell early next week, elevating surf along north and west facing.
A series of small, medium to long period south to southwest swells will continue to filter into the area through the rest of the week and into the weekend, keeping south-facing shores from going flat. East-facing shores surf will gradually pick up today into the weekend as trades strengthen and persist.

Fire weather

Wind speeds and afternoon minimum humidity levels will likely remain below critical fire weather thresholds this week. Unstable conditions will produce increasing wet weather trends across the state into Saturday. Locally heavy rain and thunderstorms are possible during this time period. Temperature inversion heights near Maui and the Big Island will range from the 7,500 to 8,500 feet elevation range today.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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