textproduct: Honolulu

SYNOPSIS

Moderate easterly trade winds are expected to continue throughout the week. An upper level trough approaching the islands will deepen into an upper low near Kauai by Tuesday. This upper disturbance will pass by the islands, then linger northeast of the state throughout the week. This will result in increased clouds and showers across the region through the week. Shower activity will favor windward mountain areas in the overnight to early morning hours, with brief periods of showers drifting into leeward areas. Locations sheltered from the moderate easterly trade winds could also see increased clouds and a few showers during the afternoons.

DISCUSSION

This afternoon, GOES water vapor imagery shows a deepening trough aloft northwest of the main Hawaiian Islands. Meanwhile, high pressure at the surface centered far northeast of the main state is supporting moderate easterly trade winds across the region. Latest radar and satellite imagery shows scattered showers along primarily windward and mauka areas, though some sheltered leeward and interior locations have experienced increases in clouds and showers this afternoon as well due to localized sea breezes.

The upper level trough northwest of the islands will approach the state over the next 24 hours. As it approaches, this trough is forecast to develop into a weak closed low aloft near Kauai by Tuesday. Further destabilization will occur as temperature inversion heights rise and clouds heights deepen. Therefore, expect enhanced trade wind shower activity throughout this period.

The developing low aloft will drift eastward on Tuesday, but then is expected to linger northeast of the state for several days thereafter. With this upper disturbance lingering nearby, a continued wet trade wind weather pattern will continue for much of the rest of the week. These showers will typically favor windward and mountain slopes, especially during the overnight through early morning hours. Trades will maintain at moderate speeds throughout the week, so sheltered leeward areas could also see increases in afternoon clouds and a few showers as localized sea breezes develop each day.

AVIATION

Moderate to locally breezy trade winds will continue during the next couple of days. A few briefly heavy showers can be expected through over the next 24 hours or so as an upper level trough moves across the region. No AIRMETs are currently in effect this afternoon, though guidance suggests mountain obscuration could develop this evening, mainly on windward Kauai. Expect more extensive interior clouds and showers on the Big Island Tuesday afternoon as the upper trough passes overhead.

MARINE

Moderate to fresh east-northeasterly trades will continue through Tuesday, then strengthen Tuesday night or Wednesday as a weak trough currently traversing the main Hawaiian islands shifts to the west and a ridge builds north of the state. This will likely correspond to Small Craft Advisory winds across the typically windier waters surrounding Maui County and the Big Island beginning by Wednesday.

Surf along exposed north- and west-facing shores eases tonight as a northwest swell fades. However, a small bump in surf is expected through the day on Tuesday with the arrival of a small northwest swell. An upward trend is expected during the second half of the week as another northwest swell arrives. Looking further ahead, a storm-force low east of Japan will send a moderate, longer-period northwest swell toward the islands for Friday and Saturday, with surf heights potentially approaching advisory levels along exposed north and west facing shores.

Surf along south-facing shores will remain small through much of the week, with mainly background south to southwest swell expected. Another south-southwest pulse may arrive by this weekend from recent activity within our swell window east of New Zealand, providing a small increase in surf.

Surf along east-facing shores will remain relatively small and choppy through midweek, with a slight rise possible later in the week as trades strengthen.

HFO WATCHES/WARNINGS/ADVISORIES

None.