NCEP/EMC Tracking of Cyclogenesis in Models

1. Purpose

The purpose of this site is to monitor the ability of various numerical weather prediction models from NWP centers around the would to develop both extratropical and tropical cyclones. Currently, the site contains track plots from various models, including the NCEP GFS, NCEP NAM, NCEP global ensemble, NCEP short range ensemble (SREF), UKMET and NOGAPS models, Canadian high resolution model and ensemble, ECMWF model and ensemble. The plan is to eventually include performance and verification statistics as well.

As a new addition to the forecst cyclone tracks, the analysis cyclone tracks in the extra-tropical regions for past 10 days are also displayed.

2. Determination of tracks

All tracks included on this site are derived from GRIB files operationally available within NCEP and are determined using the operational NCEP cyclone tracking software.

Briefly, for tropical cyclones, 7 parameters are tracked, including the relative vorticity maximum, geopotential height minimum and wind speed minimum at both 850 and 700 hPa, as well as the minimum in sea level pressure. These 7 parameters are averaged together to provide an average position fix at each forecast hour.

Since extratropical cyclones are generally not nearly as vertically coherent as their tropical counterparts, using parameters from 3 different levels of the atmosphere would muddy the tracking picture. Therefore, when tracking is done specifically for extratropical cyclones, only mslp is tracked. In order to avoid tracking weak, transient disturbances (either real or artifacts of model noise), 2 constraints have been added to the tracking criteria in order for a found disturbance to be reported as being a tracked storm: (1) the storm must live for at least 24 hours within a forecast, and (2) the storm must maintain a closed mslp contour, using a 1 hPa contour interval.

3. Updates

Track plots are being updated continuously as operational model data are ingested at NCEP.

4. Other resources

ECMWF tropical cyclone trajectory forecast products
UK Met Office tropical cyclone tracks
Naval Research Laboratory TC forecast system
Guide to Tropical Cyclone Forecasting
NCEP/EMC Cyclogenesis Tracking

With any questions/suggestions about this page, please contact:
Guang Ping Lou
Geoff DiMego
Tim Marchok

Date of last update: July 2010