65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

Forecasting Tropical Cyclone Genesis/Development Using an Ensemble of High Resolution
Deterministic Global Models – Results from the HFIP 2010 Summer Demo
Mike Fiorino
(Michael.Fiorino@noaa.gov)
NOAA/ESRL/Global Systems Division
Forecasters at the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center
(NHC) have, over the past several years, used medium (72-120 h)-to-long-range (5-8 d) global
model forecasts to qualitatively assess the potential for tropical cyclone (TC) formation. The
general finding is that if the better-performing global models (ECMWF, GFS and UKMO) all
generate a surface trough, in roughly the same location, with significant 850 mb relative vorticity
and strong precipitation, then a TC is likely to occur.
For the 2010 HFIP summer demo, we applied the 'genesis' version of the GFDL TC tracker to
quantitatively measure the genesis forecasts of six high-resolution global models available to
JWTC/NHC, namely the NCEP GFS (dx ~30km), FNMOC NOGAPS (dx ~45km), ECMWF IFS
(dx ~20km), CMC GEM (dx ~60 km), UKMO UM (dx ~30 km) and the ESRL FIM (dx=30km).
An objective genesis forecast scheme depends critically on the definition of genesis, in both the
atmosphere and in the models.
For the HFIP demo, genesis is defined from an operational perspective according to USPACOM
INST 0539.1 and the NHOP that require JTWC/NHC issue warnings/advisories for all "tropical
cyclones" (WMO definition) in their AOR. Thus, the first warning/advisory is issued when a
system reaches tropical depression strength (typically Vmax = 25 kt) and from this genesis point,
we define a 30-h 'genesis period' so as to give 00/12UTC models three chances to forecast
genesis. A successful genesis forecast is when a model 'genesis' storm (cyclones that formed
during the integration and not model tracks of existing TCs) matches an actual TC during the
genesis period.
Results from the 2010 northern Hemisphere season are presented by basin (NIO, WPAC, EPAC
and LANT); the main finding is that for systems that eventually reach hurricane strength, the
better TC forecast models (ECMWF and GFS) successfully forecast genesis at day 5 about 65%
of the time. We also use the genesis forecasts to diagnose spurious model storms or 'spuricanes'
and how these false alarms depend on the model convective parametrization. Finally, the 2011
HFIP stream 1.5 web page will be previewed.
Session 6 – Page 6