Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 726 AM EST Mon Feb 18 2019 Valid 00Z Tue Feb 19 2019 - 00Z Tue Feb 26 2019 Consensus continues to strengthen regarding the heavy rainfall threat expected over the eastern islands and the Big Island in particular through at least Tuesday. The upper low initially northwest of the main islands will wobble westward into early Tuesday and then rapidly eject northeastward in response to upstream shortwave energy. As this upper level evolution takes place, an axis of considerable deep moisture to the east will be pulled westward into the eastern islands and one or more embedded weak surface waves may track northward. Multiple guidance sources suggest the Big Island will see precipitable water values reach at least 3-4 standard deviations above climatology during Tuesday and perhaps into early Wednesday. In addition today the models appear to be showing a more coherent signal for the magnitude of this event in terms of their rainfall forecasts, while guidance in general has been consistent for multiple days with the arrival of high precipitable water values. Rainfall should trend somewhat lighter after Tuesday night/early Wednesday but it may take the passage of a weak shortwave Thursday before a more noticeable drying trend occurs. There is still some debate over extent/timing of the drier air with the ECMWF still on the quick side with the drying trend, GFS slowest and the GEFS/ECMWF means between the two. For a single deterministic forecast an average of the ensemble means would provide the best stability. During the weekend and early next week enough high pressure will likely build northwest and north of the state to promote a return of northeasterly winds and a tendency for showers to focus over windward terrain. However guidance differs on the precise details of high pressure with below average confidence in a specific solution. Rausch