Photo Credit: Brendan Stephen

West Kaua’i

Today: Cloudy and windy. Numerous showers in the morning, then occasional showers in the afternoon. Highs around 78 near the shore to around 64 above 3000 feet. Northwest winds 10 to 30 mph increasing to 20 to 30 mph in the afternoon. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 59 near the shore to around 49 above 3000 feet. North winds 10 to 25 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly sunny with scattered showers. Highs around 76 near the shore to around 62 above 3000 feet. North winds 10 to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 80. Northwest winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 58. Northwest winds 10 to 20 mph. Chance of rain 30 percent.

Friday: Mostly sunny. Isolated showers in the morning. Highs 71 to 77. North winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Cloudy and breezy. Numerous showers in the morning, then occasional showers in the afternoon. Highs 66 to 72 in the valleys to around 57 above 4000 feet. Northwest winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 51 to 57 in the valleys to around 46 above 4000 feet. Northwest winds 10 to 25 mph. Chance of rain 70 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 63 to 70 in the valleys to around 54 above 4000 feet. North winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Cloudy and breezy. Numerous showers in the morning, then occasional showers in the afternoon. Highs 68 to 77. West winds 10 to 25 mph shifting to the northwest 20 to 25 mph in the afternoon. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 52 to 60. Northwest winds 10 to 25 mph. Chance of rain 70 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 65 to 75. North winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Windy. Partly sunny with scattered showers in the morning, then cloudy with occasional showers in the afternoon. Highs 66 to 77. West winds up to 25 mph shifting to the northwest in the afternoon. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 51 to 63. Northwest winds 10 to 25 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 63 to 74. North winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A front rapidly approaching Kauai will move down the island chain today and tonight, delivering gusty west to northwest winds, brief bouts of heavy rainfall, and rather cool conditions. Mainly dry and pleasant conditions will prevail Friday night through Monday. Another front will approach the islands early next week.

Discussion

The main Hawaiian Islands lie in a benign gap between an old front just east of the Big Island and a developing front rapidly approaching Kauai from the northwest. Mostly clear skies and light westerly flow dominate the smaller islands this morning, while light southwesterlies persist around the Big Island. Radar shows scant rainfall across the state, with most of it occurring over water just northwest of Oahu and across Maui County leeward waters. All of this is about to change.
Models show gusty winds will move in today and tonight as a developing low sends the front northwest of Kauai rapidly down the island chain. Moisture along the front will not be deep, lowering flood concerns, but a strong jet streak driving the front may enhance associated showers. The post frontal air mass may cause surface dew points plummet into the low to mid 50s. As the front reaches Kauai later this morning, strengthening westerly winds and decreasing stability may produce wind gusts near 40 mph over and downwind of terrain from Kauai to Maui. Higher gusts, near 50 mph, may occur within enhanced showers as strong winds aloft mix down to the surface. We will monitor conditions to see whether Wind Advisories are needed for lower elevations. The highest chances for strong gusts will be along and just behind the front as it passes over Kauai later this morning, Oahu late this afternoon, and Maui County this evening. Strong winds will also affect the summits of the Big Island and Haleakala on Maui. A High Wind Warning remains in effect for these summit areas for increasing winds this morning and for westerly winds above 60 mph later later today into Friday morning.
A noticeably cool air mass will fill in behind the front on Friday as lingering showers affect mainly northern slopes. Highs will only reach the mid 70s, and dew points in the moderate to breezy northerly winds may fall below 50 deg F, providing a chill to the air. Strong summit level winds will slowly diminish. Dry conditions will prevail during the weekend. Northerly winds will ease on Saturday and switch to light southerlies on Sunday and Monday as another front approaches the region. Models show this next front may reach Kauai sometime Wednesday morning.

Aviation

Isolated to scattered showers continue to move across the state early this morning as a surface trough advances eastward over the island chain. Light winds will pick up to become moderate to breezy by mid to late morning in advance of the next cold front. This fast moving front will usher in strong northwest winds and scattered to numerous showers into Kauai by this afternoon and quickly spread eastward down the island chain through the day into tonight. In addition, an associated mid/upper level jet moving over Hawaii midday today will also bring the potential for moderate to severe turbulence this afternoon into tonight.
AIRMET Tango is in effect for moderate low level turbulence below 090 downwind of the terrain across the eastern end of the state. VAD wind profiles are picking up on winds around ridgetop anywhere between 25 to 50 knots. This AIRMET will be needed through the morning and then will likely be expanded across the state later today as the fast moving cold front moves through.

Marine

A weakening near stationary boundary resides across the eastern waters as a trough begins to advance into the western waters. Gentle to moderate westerly winds will occur through the morning hours before restrengthening behind the next passing strong cold front through the day. This front is currently entering our far northwest offshore waters and is quickly moving east southeast at 30 knots. The front should pass across the near coastal waters and be in the eastern waters during the pre-dawn Friday morning hours. Sustained post-frontal winds will easily achieve strong to near gale force magnitudes with occasional gale force gusts from later this morning into Friday…strongest from the Kaiwi Channel westward. Winds will weaken back to high-end moderate to fresh speeds by Friday evening. The combination of these post- frontal strong to near gale force winds and high seas from the passage of large north or northwest swells (see surf discussion below) will maintain a Small Craft Advisory (SCA) for both winds and seas that will be in effect for all waters (except better protected Maalaea Bay) through Friday afternoon.
A moderate, medium period northwest (330 degree) swell is continuing to decline this morning. A complicated swell set up will occur in the coming days as a series of northwest and north swells will arrive from different sources. First, as the ongoing northwest swell fades through the day, a large, medium period northwest (330-340 degree) swell will come in behind it tonight through Friday morning (from the strong cold front mentioned above) and this will lift surf back up to High Surf Advisory (HSA) heights along smaller island north and west-facing shores Friday morning. A HSA is effect from Noon today through early Saturday morning for the north and west facing shores of the smaller islands (exception being only north-facing Maui shores). A north swell will also arrive during Friday that will generated by a gale force low north of the state. This north-veering-northeast swell into Saturday will be large, but of medium period due to the close proximity of the fetch region along the backside of the gale low. The combined swells will significantly pick up surf along the north and west-facing shores to either high-end HSA or low- end High Surf Warning levels tonight through Friday…and is dependent upon the timing of the swell arrival along with any destructive, cancellation effects. The north swell will veer more northeasterly late Friday as the gale low drifts slowly eastward. Surf along west-facing shores should drop below HSA thresholds Saturday while northern exposures will hold on to HSA heights through Saturday. Surf along east-facing shores will remain relatively small through the week with the exception of those areas exposed to north northeast swell wrap.
Tides are currently running about 0.35 to 0.75 feet above normal. Relatively high astronomical tides in the near 3 foot range (2.7 to near 2.9 feet), with a large north swell run up added to these already above normal water levels, will likely produce minor, nuisance coastal flooding within low lying flood-prone areas during the early morning pre-dawn high tide times the next few days. Additional impacts with these north swells may include harbor surges within both Kahului and Hilo Harbors from Friday evening through Saturday night.

HFO Watches/Warnings/Advisories

High Surf Advisory from noon today to 6 AM HST Saturday for Niihau, Kauai Leeward, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Koolau Windward, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
High Wind Warning until 6 PM HST Friday for Haleakala Summit, Big Island Summits.
Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters except Maalaea Bay,

Data Courtesy of NOAA.gov