Swell Matrix

Area Forecast Discussion

National Weather Service Honolulu Hi

340 pm hst Sun aug 1 2021

Synopsis

Strong high pressure far north northeast of the area will provide for breezy to locally windy trade winds through Monday. Winds will drop off slightly beginning Tuesday as the high weakens just a bit. Generally dry conditions will prevail into Tuesday with an uptick in showers expected by the middle of the week favoring windward and mauka areas.

Discussion

Satellite imagery currently shows random patches of low stable clouds moving westward in the trades. Also, a wildfire in the Kohala area on the Big Island is sending smoke westward into the North Kona District. Radar imagery shows very little in the way of showers across the area with just a few light showers seen moving into windward and mauka areas and primarily over the Big Island with a few showers seen over the Kona slopes. Generally dry conditions prevail across the rest of the state.

A 1033 mb high is centered far north northeast of the area. The tight pressure gradient south of the high along with strong low level temperature inversions around 6500 feet, will cause trade winds to be breezy to locally windy across portions of the state. These breezy to locally windy conditions are expected to prevail through Monday then slowly decrease Tuesday through Saturday as the high to the north weakens allowing the pressure gradient to relax just a bit.

The airmass will remain rather dry and stable over the next couple of days with strong low level inversions remaining in place as a ridge aloft dominates. Basically dry weather will prevail with just some brief passing showers possible over windward and mauka areas with some upslope showers possible over the Kona slopes during the afternoon and evening hours. Beginning Tuesday, a weak mid level trough will drop down near the east end of the island chain which will raise inversion heights. Some increase in shower activity is expected especially for windward and mauka areas and will be highly dependent on incoming moisture availability.

Aviation

Moderate to locally strong trade winds will persist. The air mass over the state will also remain stable with an inversion aloft between 05 kft and 07 kft. AIRMET Tango for low level turbulence downstream of higher terrain below 08 kft remains in effect.

Low topped stratocumulus and scattered showers will favor north and east facing slopes and coasts. Brief MVFR CIG and VIS are likely in passing showers. Mountain obscuration could become an issue for Windward Big Island or Kauai late tonight. Otherwise VFR conditions will prevail.

Low-level wind shear characteristic of strong trade winds is possible in favored locations, especially overnight. Central and South Maui including PHOG are of particular concern.

Finally, areas of reduced visibility in smoke are detectable across Leeward Big Island north of Kona due to the Waikoloa wildfire.

Marine

Today's ASCAT pass missed the islands, however wind reports from nearshore buoys and coastal locations indicate strong trades continuing. High pressure remains north of the islands driving the strong trades across the region. As such, we are leaving the Gale Warning up until 6pm today for the waters near Maui County and the Big Island where the strongest winds are typically found. Anticipate the Gale Warning being replaced by the Small Craft Advisory (SCA) shortly before 6pm. A SCA remains in place for the remaining waters. Around 6pm, the SCA will then be in place for all coastal waters through tonight. Winds are expected to gradually weaken starting tonight, and by tomorrow morning, waters near Kauai and Oahu are expected to be below SCA. The SCA will continue for the remaining waters tomorrow and tomorrow night. By Tuesday, the current forecast will have SCA only in the typically windier waters near Maui County and the Big Island, and those winds will likely stick around through much of the week.

The rough, slightly elevated surf continues along east facing shores driven by the strong trade winds. Expect surf along the east facing shores to persist into Tuesday, before decreasing to near the summertime average mid-week as the trade winds weaken slightly. Some residual south-southeast swell energy will continue to keep south facing shores from going flat from Monday through mid-week. The forecast guidance shows a small southwest swell arriving next Friday, which may provide a small boost in surf heights along exposed south facing shores heading into next weekend. Expect nearly flat conditions along most north and west facing shores this week.

Watches, Warnings, Advisories

Wind Advisory until 6 PM HST this evening for Lanai Mauka-Maui Leeward West-Kohala-Big Island Interior-Lanai Windward-Lanai Leeward-Maui Central Valley North-Maui Central Valley South-Big Island South-Big Island Southeast.

Small Craft Advisory from 6 PM this evening to 6 AM HST Tuesday for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.

Gale Warning until 6 PM HST this evening for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.

Small Craft Advisory until 6 AM HST Tuesday for Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Big Island Windward Waters.

Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters.

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