Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
214 AM EDT Wed Jul 22 2020

Valid 00Z Thu Jul 23 2020 - 00Z Thu Jul 30 2020

...Douglas forecast to approach Hawaii as a tropical storm over
the weekend...

A broad weakness in the upper-level ridge will move west of Hawaii
by Thursday, with initially light trades gradually increasing
through late week as the feature moves away. The most significant
aspect of the forecast for Hawaii over the next week continues to
be the eventual track of Tropical Storm Douglas, and any potential
impacts on Hawaii. The National Hurricane Center is forecasting
the system to be near approximately 19N/153W (approximately 120
miles east of the Big Island) Sunday afternoon, as a tropical
storm. Consensus among models and ensembles surrounding this track
is good, with ensemble members among both the ECENS and GEFS quite
well-clustered. Beyond the official 5-day forecast track from the
NHC, models generally continue a westward track across the
Hawaiian Islands as the low pressure continues to weaken. Deep
moisture associated with the system could produce heavy rains as
the system passes, particularly across the Big Island, where
ensemble probabilities suggest the greatest threat for
heavy/multi-inch rainfall totals Sunday-Monday. Any shift in track
farther north or south could significantly affect potential
rainfall totals, however. The system also has the potential to
produce strong/gusty winds across Hawaii, dependent on the exact
track and how quickly the system weakens, as well as high surf.
Please refer to advisories from the National Hurricane Center for
the latest information on Tropical Storm Douglas. After the
tropical system moves west of Hawaii early next week, models
generally show drier air filtering into Hawaii, with relatively
strong trades continuing into the middle of next week.

Ryan