GFS, a review of model trends and biases, and a description of model differences and preferences. The meteorologist reviews how the suite of models from the latest forecast cycle differ from each other in their forecasts of significant features, and makes a preference based upon all relevant current information. Surface analysis The WPC Surface Analysis is part of the NWS Unified Surface Analysis and a collaborative effort with the Ocean Prediction Center, the National Hurricane Center, and the Honolulu Weather Forecast Office. The WPC focuses on the synoptic and mesoscale features over North America, primarily north of 31N. The surface analysis is a manual analysis of surface fronts and pressure over North America and adjacent oceans performed every three hours. The analysis utilizes a variety of weather data in addition to observations of surface weather conditions, such as upper air observations, global satellite imagery, Doppler radar, and model mass fields to ensure that the product is meteorologically consistent. Tropical cyclone forecast duties The WPC is the official backup center to the National Hurricane Center (NHC). In this capacity, the WPC is responsible for issuing all tropical cyclone products, including discussions, graphics and watches and warnings that would normally be issued by the NHC for any tropical system in the Atlantic Ocean, if NHC is unable to so. During the tropical weather season which runs from May 15 – November 30, the WPC has several other routine duties pertaining to tropical weather forecasting. Through 2008, WPC provided track forecast guidance to the NHC whenever there is a tropical cyclone in the Atlantic Ocean basin west of 60W longitude. As required, this guidance is provided to the NHC four times daily for use in the tropical cyclone package issued by the NHC at 0300 UTC, 0900 UTC, 1500 UTC and 2100 UTC. The WPC participates in the Hurricane Hotline call with the NHC and other forecast offices and government agencies at 1700 UTC for tropical cyclones in the Atlantic Ocean basin west of 60W longitude. Also, points for days 6 and 7 for existing tropical cyclones east of 140W longitude, and days 3–7 to possible future tropical cyclones, are coordinated between the medium range pressures desk and NHC each day at 1700 UTC during the hurricane season. This coordination call began between the Extended Forecast Section and the Miami Hurricane Warning Office prior to 1959. Within the WPC tropical program, the lead