Relatively weak trades will continue through Friday, with increasing wind speeds this weekend. An upper low and midlevel trough will bring an increased chance of showers to the western end of the state over the next few days. Showers will shift to the eastern end of the state this weekend as an area of tropical moisture passes by.
An upper low to the west and associated midlevel trough will linger over the next couple of days and enhance incoming trade wind showers, particularly across the western half of the state. Cooling aloft across the west has eroded the trade wind inversion with 00Z soundings show a weaker and elevated inversion at Lihue compared to Hilo. The upper low is forecast to lift away to the north on Friday returning more stable conditions to the area.
Trades will be weaker than average through Thursday as the remnant of former tropical cyclone Genevieve lingers between the subtropical high and Hawaii. As a result, trades will be weak and localized sea breezes will bring interior and leeward cloud build ups each afternoon. Across Kauai and Oahu, scattered showers may develop during the afternoons due to the instability and low level moisture from the upper low/trough described earlier. Trades will increase this weekend, doing away with most of the sea breeze effects.
The weekend guidance suggests a plume of moisture coming either over or very close to Maui and Big Island. While most of the plume will pass south of the area, the northern periphery of it is expected to skirt by and bring additional showers to windward sides of both islands.
A weak high pressure ridge far north of the state will keep gentle trade winds in the forecast. An upper level low and assoicated low level inverted trough will remain over the western end of the state, enhancing trade wind showers. Otherwise hybrid pattern of trade wind clouds and showers will focus over windward and mauka areas with afternoon seabreezes increasing cloud and showers over leeward and interior areas. Land breezes will clear clouds and showers overnight for the sheltered areas.
AIRMET Sierra in effect for mountain obscuration above 020 for the entire island of Kauai and for windward and mauka areas of Oahu and Molokai. Periods of MVFR conditions are possible overnight for windward and mauka areas for the rest of the state. Otherwise expect mostly VFR.
Will continue to monitor all observations for possible AIRMET Tango due to upper level turbulence as the upper level low and associated jet approaches Kauai from the northwest. In addition will also keep monitoring for possible AIRMET Zulu due to light icing above the freezing level within the upper level cloud band.
No significant changes to the forecast or the forecast philosophy with the afternoon package. The remnants of former Tropical Cyclone Genevieve are more than 900 miles northeast of the islands this afternoon, and continue to lift northward and weaken. A west to east oriented front remains well north of the islands. These systems are helping to limit trade wind speeds across the islands. As they dissipate and move away from the islands, high pressure north of the islands will help trades to restrengthen to locally breezy levels by the end of the week. This could then bring some Small Craft Advisory level winds to the more typical windier areas late in the week or over the weekend.
Surf along south-facing shores will remain below seasonal averages through much of this week, though occasional small fluctuations can be expected as small background swells move through. By this Saturday, a small, long period south swell is expected to arrive, followed by a series of reinforcing south swells that will boost surf heights to near or above seasonal averages into next week.
Small, medium period easterly swell generated from former Tropical Cyclone Genevieve continues to linger, but will gradually ease for the next couple of days. Choppy conditions will remain, generated by the moderate trade winds.
Surf along north facing and west shores will remain flat to tiny through the forecast period, except for areas exposed to the easterly trade wrap.
None.
