What the forecast actually says — NWS Area Forecast Discussions, decoded into plain English.
Area Forecast Discussion · National Weather Service Honolulu (HFO) · issued Friday, November 13 at 3:42 AM HST.
Revised in 14 passages since the 8:05 PM discussion. See every revision.
Synopsis
A weakening high pressure ridge north of the Hawaiian Islands will keep trade wind speeds on the decreasing trend lasting into Saturday, then ridge and wind speeds strengthen from Saturday afternoon into early next week. Passing showers are possibly over windward and mountain areas during this time period, mainly during the overnight to early morning hours. The next best chance for statewide rainfall may develop from Monday into Tuesday of next week, as the cloud remnants from an old cold front drift across the islands on the trade winds.
Discussion
A combination of satellite and radar imagery this morning paints a wetter than normal picture for the windward mountain slopes of all Hawaiian Islands this morning. Two parts to this passing shower story are upper air soundings from 2 AM HST (12Z) this morning measuring trade wind temperature inversion heights in the 6,000 to 7,000 foot range and deep easterly trade winds above the 30,000 foot level. Cloud heights remain elevated allowing passing showers to continue mainly during the overnight to early morning hours, favoring the windward mountain areas.
In the large scale pressure pattern forecast model guidance continues to show the high pressure system north of the islands weakening into early Saturday. Trade wind speeds will trend slightly lower during this time period. A stronger high pressure system builds in north of the state from late Saturday into the first half of next week with more breezy trade winds blowing across the region. The difference in wind speeds will be subtle.
Weather wise a band of clouds associated with an old dissipated front will drift over the islands early next week from Monday night into Tuesday, increasing clouds and shower coverage. Long range model solutions are showing a weak upper low dropping into position just west of Kauai from Tuesday to Wednesday. Southeasterly winds aloft are pulling up remnants of this old frontal cloud band back over the islands along with added upper level instability. If this pattern develops as predicted by the global models, then an extended wet weather pattern may linger into next week Thursday, especially over the windward mountain slopes of Maui and the Big Island. Both the American (the American global model) model and the European (the European model) model are showing a flavor of this extended wetter pattern with the the American global model being the wetter of the two solutions. This pattern would likely produce another round of beneficial light to moderate rainfall rates.
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