textproduct: Honolulu

SYNOPSIS

A relative decrease in shower activity in the wake of a departing surface trough associated with the remnants of Norbert is expected through this weekend. Moderate to locally breezy trade winds will continue through Monday before gradually declining by midweek. Another round of enhanced moisture will arrive by next Tuesday, which should increase shower activity statewide.

DISCUSSION

This afternoons visible satellite and radar imagery shows a limited amount of shower activity relative to the past couple of days. A surface trough associated with the remnants of Tropical Cyclone Norbert continues to move westward as it exits the vicinity of the state tonight. However, an upper level trough combined with the residual moisture from Norbert has kept the environment relatively unstable, as noted by some thunderstorms occurring offshore earlier today, and over the Kona slopes of the Big Island this afternoon.

An increasing trend in stability and relatively drier air will begin this weekend, which will limit shower activity and coverage to windward and mauka areas. Kona slopes of the Big Island may still see some afternoon showers as well through the weekend, with a small chance of thunderstorms upslope due to lingering instability. However with the low confidence, have not added thunderstorms to the forecast. Trade winds will continue to blow out of the ENE-E direction at moderate to locally breezy speeds through Monday, but are expected to gradually decline by midweek.

Another influx of moisture associated with the remnants of Tropical Depression 15-E is expected to arrive by Tuesday and potentially remain through Thursday. Precipitable water values could reach up to 2.5" over the southeastern portion of the state according to global models, which is above seasonal normal. A shortwave is also expected to be within the vicinity of the islands during this time period, which could lead to some enhanced showers statewide.

The long term forecast will also be dependent on how models handle the remnants of Tropical Depression 15-E. The National Hurricane Center continues to monitor the situation, and suggests that environmental conditions are conducive for some development of the system next week. Given that there is plenty of time for this forecast to change, please continue to monitor the status of tropical cyclone development through nhc.noaa.gov, and local weather forecasts at weather.gov/hfo.

AVIATION

Minor changes were made to the forecast to adjust for some of the breezier trade winds this afternoon. Otherwise, we remain in a transition between a moist airmass with a vicinity trough to drier trades tomorrow. Mainly VFR conditions will prevail, with the potential for MVFR cloud decks and isolated showers to continue passing through the region. Stronger showers will likely bring a reduction in visibility as well, perhaps down to MVFR at times. There is a non- zero chance for isolated thunderstorms around the Kona slopes of the Big Island; however, chances are generally around 15% or less and confidence remains low to add to the TAF.

Tomorrow, drier air works into the region as breezy trade winds persist.

AIRMET SIERRA remains in effect for Kauai, Oahu, Maui, and portions of the Big Island. This is for windward exposure mountain obscuration near or above 2,500 ft. This may be able to be cancelled by the next AIRMET update.

As of 300 PM HST, no other AIRMETs are in effect.

MARINE

Trade winds will remain fresh to locally strong through at least the first half of next week. A Small Craft Advisory is in effect for the typical windy waters around Maui County and Big Island through Saturday, and will likely be extended into early next week for these waters.

Surf along south-facing shores will remain above average through the weekend. The current long-period south-southwest swell will peak this evening, then gradually decline through the weekend as the next moderate, long-period south swell fills in late Saturday through Monday, possibly nearing advisory criteria.

Moderate surf along east-facing shores will persist over the next several days as fresh to locally strong trades continue. Surf along north-facing shores will remain flat to tiny, with a minor bump possible Tuesday into Wednesday next week.

FIRE WEATHER

Fire weather risk remains low due to residual moisture from the remnants of Norbert. The inversion is sitting roughly around 7kft, but is expected to lower over the weekend. Moderate to locally breezy trade winds are expected through Monday, and should filter in some relatively drier air for that time period.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Saturday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.