Sunday, 22 January 2012
A Comparison of Model Precipitation Forecasts for Hurricane Ida (2009)
Hall E (New Orleans Convention Center )
Hurricane Ida (2009) was a long-lived late-season hurricane (4 November – 10 November) that caused substantial amounts of rainfall along the Mid-Atlantic coast. At its peak, Ida was a Category 2 hurricane with maximum sustained wind speeds of 90 knots (~46 m/s), but quickly weakened to a tropical storm due to cold ocean temperatures and strong vertical shear. After making landfall on 10 November as a tropical storm, Ida quickly became an extratropical cyclone, which merged with an occluded front and spawned a new upper-level cyclone. Due to a low-level anticyclone in the northeast US, Ida's remnants stalled, producing large amounts of rainfall along the East coast, with a maximum of 18 inches (~46 cm) in southeast Virginia. As of July 2011, Hurricane Ida is the most recent significant tropical cyclone to have made landfall on the United States, causing $300+ million in damage from flooding, winds, and storm surge. Ida's genesis probability was not forecast as “medium” (30-50%) until just 18 hours before genesis and only shortly before Ida's landfall did models have reasonably accurate precipitation forecasts. This study looks at precipitation forecasts from 09 November and 11 November from the NAM, GFS, and HWRF out to 72 hours from initialization time. Each models' quantitative precipitation forecast is analyzed and evaluated against each other as well as the actual observed rainfall.