Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 827 AM EDT Mon Sep 25 2017 Valid 00Z Tue Sep 26 2017 - 00Z Tue Oct 03 2017 To commence the forecast period, a closed upper low will be spinning along 150W longitude, just east of the Hawai`ian island chain. While initially drifting farther east in time, there are suggestions the circulation could swing back toward the west. The solutions are quite variable suggesting low confidence in eventual placement. In addition to this feature, a much more robust closed low is expected to detach from the prevailing westerlies during the upcoming weekend with a position along or just east of the International Dateline. By Sunday afternoon, the 06Z GFS/00Z ECMWF are literally 10 degrees apart in longitude from one another with even more scatter among their individual ensemble members. However, there is agreement in shifting this negative height anomaly westward, away from the region, moving into early next week. At the surface, given an initially weak pressure gradient across the central Pacific, east-northeasterly winds around 10 to occasionally 15 knots is expected through much of the week. By Friday into the weekend, warm advection in advance of the next system dropping southward should lead to a more southeasterly flow regime. As this particular feature begins to retrograde, operational/ensemble guidance agree on building a strong surface anticyclone north of Hawai`i by Sunday onward leading to strengthening trades. Regarding precipitation, windward showers will be the norm with a potential uptick in coverage by mid-week as a slug of higher precipitable waters values swings westward through the region. Any rainfall with the frontal zone descending from the mid-latitudes should remain well west of Hawai`i. And given the presence of the upper low lingering to the east, some additional showers may spawn. Rubin-Oster