Photo Credit: Jason Weingardt

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs around 78 near the shore to around 66 above 3000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 57 above 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly sunny with isolated showers. Highs around 78 near the shore to around 66 above 3000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

South Kaua’i

Today: Windy. Partly sunny with scattered showers. Highs around 77. Northeast winds 15 to 30 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 69. East winds 20 to 25 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs around 77. East winds 20 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Windy. Mostly cloudy with scattered showers. Highs 65 to 73 in the valleys to around 60 above 4000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Windy. Numerous showers in the evening, then occasional showers after midnight. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds 15 to 30 mph. Chance of rain 90 percent.

Monday: Partly sunny. Windy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 65 to 73 in the valleys to around 60 above 4000 feet. East winds 15 to 30 mph. Chance of rain 80 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 70 to 77. East winds up to 20 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 60 to 69. East winds 10 to 25 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 70 to 77. East winds 15 to 25 mph. Chance of rain 50 percent.

East Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs 70 to 77. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 58 to 70. East winds 15 to 25 mph. Chance of rain 70 percent.

Monday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 77. East winds 20 to 25 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Strong high pressure building to the north of the islands will bring an increase in trade winds later today into Monday, with windy conditions lingering through Thursday. Although showers will be somewhat limited today, passing and fairly frequent showers can be expected over windward areas this week, with a few showers reaching leeward communities. Some decrease in wind is expected by the end of the week as the high moves away, and a front approaches.

Discussion

A very strong (1047 mb) surface high pressure cell located about 1600 miles N of Kauai is supporting breezy to locally strong trade winds. Morning soundings indicate that a subsidence inversion is in place near 8000' on Kauai, where PWAT is down to 0.9″, but it is elevated and weakened to near 10000' on the Big Island, with PWAT near 1.2″. Radar shows limited showers over and upstream of the smaller islands, with diminished overnight shower coverage as dew points lowered into the upper 50's in many areas. Showers have been most persistent over windward slopes of the Big Island, with a few small heavy rain cores noted. Some of the wetter locations on windward Big Island slopes have recorded up to 1.5″ of rain over the past 12 hours, but upstream showers look to be trending down now. Water vapor imagery and latest model analyses show a weak, E-W oriented trough axis aloft very close to the Big Island, and this feature may be the reason for the recent increased showers/elevated inversion.
An area of broken showery low clouds extends about 100 miles E and SE of the Big Island, with few to scattered low clouds prevailing immediately upstream of the other islands. Model guidance indicates the bulk of this nearby moisture will pass SE of the Big Island this morning, with windward shower coverage expected to diminish through this afternoon as the trough aloft moves E. In general, a breezy to locally windy day, with just a few windward showers. By this evening, guidance depicts that a subtle increase in moisture currently NE of the islands will arrive, bringing some increase in windward showers into Monday.
The surface high will move slowly SSE and toward the islands over the next several days, bringing an increase in trade wind speeds. Although the central pressure of the high will be easing into the upper 1030's by Tuesday, the associated pressure gradient over the islands will tighten. This will lead to windy conditions, and likely the issuance of a Wind Advisory, at least for parts of the state. Winds look to be in this range from tonight/Monday into Thursday. A low aloft is forecast to deepen to the E of the islands at the same time, likely leading to a destabilization of the incoming low clouds. This means that a wet and windy period can be expected, with frequent windward showers occasionally spreading some moisture leeward.
Long range guidance alludes to a pattern change that would lead to weaker winds by the end of the week as a front approaches from the NW and the high moves away from the islands. Although confidence is not particularly high due to the longer time range, there is considerable model agreement that the front will move over the island chain the following Monday/Tuesday.

Aviation

Breezy to locally strong northeast trade winds will continue to deliver scattered moderate showers to the islands, with a focus over windward areas. Some of these passing showers will bring brief MVFR conditions, otherwise VFR conditions will prevail.
AIRMET Tango remains in effect for both moderate low level and high level turbulence. Low level mechanical turbulence downstream of higher terrain is expected to persist through 24 hours and possibly beyond. High level turbulence is expected to end toward morning as the upper level jet weakens and shifts southward.

Marine

A strong high pressure system building in far north of the Hawaiian Islands will increase trade winds once again into the strong to gale range this week. A Gale Watch was issued this morning for windier eastern waters and channels near Maui and the Big Island through Wednesday. A Small Craft Advisory remains in effect for all other coastal waters and channels through Wednesday.
The strong trade winds over the region will maintain a large east to west upstream fetch area and continue to produce rough trade wind swell affecting exposed east facing shores through much of this week. The current High Surf Advisory (HSA) for east facing shores remains in effect through Tuesday afternoon. This HSA may need to be extended in time with high surf forecast to continue along east facing shores at least into Thursday.
A small northwest swell (310-320 degrees) will slowly decline through the first half of this week. Surf heights along north and west facing shores will remain below normal through the week. Another small longer period northwest swell (310-320 degrees) will build into the islands from Thursday night into Friday morning proving a small boost to surf heights along north and west facing shores lasting into the weekend. South shore surf heights will see a slight increase into Monday due to the arrival of a small long period south swell, then dropping back to background levels from Tuesday onward.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Tuesday for east facing shores of Kauai, Oahu, Molokai, Maui, and Big Island.
Small Craft Advisory until 6 PM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Watch from this evening through Wednesday afternoon for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov