Improving Tidal Simulations in the NWS’ Extratropical Storm Surge Model along the Coasts of Alaska and the Gulf of Mexico

The National Weather Service’s (NWS) Meteorological Development Laboratory (MDL) developed the Extra-Tropical Storm Surge (ETSS) model in 1995. Since then, MDL has enhanced the ETSS model to operationally provide deterministic inundation guidance four times a day based on storm surge and tide in coastal areas along the United States’ Eastern and Western Seaboards, the Gulf of Mexico and Alaska.

Tidal simulation along the coasts of Alaska is particularly challenging due to a sparsity of active water level observational sites and long term tidal records, compounded by the cost and difficulty of attaining bathymetric and topographic data. However, the correct tidal phase (i.e. timing) is crucial for inundation guidance as it determines whether the surge coincides with low or high tide. Users of ETSS guidance have reported tidal phase shift problems along Alaska’s Bering Sea coastline and the west coast of Florida.

MDL addressed these issues in the latest ETSS implementation by: (a) incorporating a new tidal database for Alaska, and (b) introducing a new tide algorithm. This paper describes the details of these efforts and provides verification of the results for several case studies.