Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 830 AM EDT Wed Apr 26 2017 Valid 00Z Thu Apr 27 2017 - 00Z Thu May 04 2017 The initial synoptic pattern supports broad upper ridging extending from the Hawai`ian island chain eastward toward 135W longitude. As time proceeds forward, amplified flow upstream will trek eastward with the base of the trough reaching the state by Friday morning. At this point the flow regime becomes rather blocked in nature as a closed low sags southward from the mid-latitudes. The circulation center is forecast to continue its slow migration southward over the weekend with the upper low generally over 25N/155W by 30/1800Z. There is one notable outlier which is the 00Z UKMET given its displacement to the southwest of the model consensus. Eventually the negative height anomaly will reach Hawai`i by late Sunday/early Monday with gradual shearing along with an eventual shift eastward toward the middle of next week. At the surface, with an anticyclone centered northeast of the region, moderate trade winds are to be expected before a shift in the pattern is evident. With the associated cold front approaching from the northwest, a large change in the surface pattern is forecast with north-northeasterly flow prevailing within the cool sector of the cyclone. Expected winds will be in the 15 to 20 knot range with this cold advection moving from north to south across the state. Gradually winds will become more cyclonic across the region as the vertically stacked system moves directly overhead. As the surface gradients weaken, a decrease in the wind field is likely through the remainder of the period. In terms of precipitation, expect the most active times to be as the circulation center moves directly over the state. Rubin-Oster