The Navy Operational Global Atmospheric Prediction System (NOGAPS) is a numerical weather prediction model developed by the Naval Research Lab (NRL) and run operationally at the Fleet Numerical Meteorology and Oceanography Center (FNMOC). NOGAPS was upgraded from a T159L24 (159-wave spectral resolution with 24 levels in the vertical) configuration to a T239L30 configuration on 18 September 2002. The corresponding Gaussian grid resolution for the T239 NOGAPS implementation equates to about 55 km horizontal spacing between grid points. Forecasts are made 4 times daily and extend to 144 hrs, using a 6-hr update cycle for data assimilation.

This paper investigates systematic tendencies and biases of NOGAPS central pressure forecasts for extratropical cyclones with central mean sea-level pressure not exceeding 1001 mb. Specifically, temporal and regional forecast biases are addressed for ocean and land lows, including deepening (pressure drop greater than -1 mb/12 hrs but less than -7.5 mb/12 hrs), rapidly deepening (pressure drop greater than -7.5 mb/12 hrs), and filling (pressure rise greater than 1 mb /12 hrs) systems. The regions of investigation include North America, Eurasia, the North Atlantic Ocean, North Pacific Ocean, and the Mediterranean Sea. The paper focuses on 48 to 96-hr forecast errors.

Results for September through May indicate NOGAPS is slow to deepen for deepening cyclones, with the tendency most apparent for rapidly deepening cyclones. This is especially evident at forecast times beyond 48 hrs. Conversely, NOGAPS is slow to fill for filling cyclones, with the exception of those in the North American region. Here, NOGAPS shows a slight tendency to over fill for filling cyclones. These tendencies are again most notable at forecast times beyond 48 hrs.