Developing oceanic lows tend to be slightly underforecast and slow to deepen with an ACPE near zero through 72 hours. Atlantic mature lows are mostly deep and slow to fill. West Pacific tropical cyclones are typically slow to move during and after transition to extra-tropical. Secondary cyclogenesis continues to be underforecast. Lee cyclogenesis off Southeast Kamchatka and Greenland is underforecast.
Surface lows forming south of the polar jet and bottom-up type of lows are slow to deepen.
These are usually mature lows which have bottomed-out and tend to be slow to fill. Instances of major overforecasting of cut-off lows may reflect the occasions where valid ship reports are sparse. The overdeepening bias is primarily associated with digging troughs over the region as opposed to west-east moving troughs. The tendency to overdeepen lows is mostly observed in the cool seasons. Sea-level pressure analyses and forecasts over the very high terrain of Greenland, Himalayas, Antarctica are suspect and should be used with caution.