Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 826 AM EDT Wed Sep 12 2018 Valid 00Z Thu Sep 13 2018 - 00Z Thu Sep 20 2018 Tropical Storm Olivia continues its motion to the west-southwest toward the eastern portion of the main Hawaiian islands, and is expected to cross the area today. As indicated in the 0900 UTC Central Pacific Hurricane Center advisory, exact motion of the low level circulation center has been erratic with some dependence on the evolution of deep convection. Although the surface low will be tracking away from the islands soon, the combination of lingering moisture over/near the islands and an upper low passing over the region will maintain the threat for locally heavy rainfall into late this week. Expect total rainfall of 5-10 inches over some areas with isolated maxima of 15 inches possible, especially in higher terrain. This rainfall could produce flash flooding. Dangerously high surf will be another hazard associated with Olivia. After Olivia's passage expect a return to trades of at least moderate strength, with lighter windward-focused shower activity from this weekend into next week given a trend toward lower precipitable water values. Exactly how much of a lower trend there is remains up for debate however, with the 00Z ECMWF showing lower PWATs than the 00Z GFS/GEFS mean. The 06Z GFS has trended a little lower. By next Wednesday there are signals for some increase in moisture from the east-southeast but at the same time upper ridging builds in from the east. Guidance shows good agreement with central Pacific surface high pressure through the weekend. Then solutions diverge with details of low pressure that may produce a break in the ridge, so confidence declines a bit for trade details after Sunday. Rausch