Hurricane Forecast Models

A Few Words on Hurricane Forecasts
Forecast Track Error
Rule of Thumb for
Forecast Track Errors:
24 hours  40 nm
48 hours  70 nm
72 hours  100 nm
Today’s 3-Day Forecast
is as good as a 1-Day
Forecast in 1990.
Intensity Error
Intensity Forecasts
are still in need of
improvement:
Rule of Thumb:
Error ± 10 kts
What’s With All the Models?
Models of Interest
• Global Models (Track)
– European Center (ECMWF): EMX, EMXI
– NOAA (GFS): GFSO
• Ensemble of Global Models (Track)
– GFS Ensemble: AEMN
– ECMWF Ensemble: Can find at Hart-FSU
• Limited Area Models (Intensity)
– HWRF
– GFDL
• “Super Ensembles” of Many Models (Track and Intensity)
– TVCN/TVCA/TVCE (acronym keeps changing)
– FSSE (Florida State, proprietary)
– ICON and IVCN: Intensity ensembles
Forecast Track Skill in 2012 (Atlantic Basin)
The Best:
FSU Super Ensemble
NHC Official Forecast
GFS Ensembles
ECMWF Ensembles
GFS
ECMWF
Intensity Skill in 2012 (Atlantic Basin)
After 24 hours,
ensembles are
clearly better.
But improvement over
reference (low skill)
forecast is only 10-20%,
compared to 50-80%
for track error.
GFS Ensemble Forecasts for Sandy
(72 hours before landfall)
ECMWF Ensemble Forecast for Sandy
(72 hours before landfall)
Why Do Ensembles Work?
• Even a perfect model (with equations that mimic
nature) will eventually go astray.
• This is a result of the sensitivity of the model to
slight errors in its initial conditions.
– We can never completely observe the atmosphere.
• By introducing “expected” errors into the initial
conditions, we can get an idea of the “spread” of
the possible forecasts, and, the mean value
becomes a very reliable forecast.
A Word on Forecast Timing
• NHC tropical storm forecasts are posted every
six hours with intermediate updates, if
needed, between forecasts.
• The time it takes to prepare the forecast
means that they are based on analysis of
earlier models (“Early Runs”).
• By the time forecast is issued, latest runs are
just coming online.
Latest Developments
HFIP-EFS
• Hurricane Forecast Improvement Project
(HFIP), Ensemble Forecast System (EFS).
• Hurricanes/TS can alter the flow in which they
are embedded. This alteration can feedback
into TS track and intensity.
• Large scale flow, which strongly impacts track,
can be resolved at resolution ∆x ≈ 15-20 km.
• Inner core dynamics, which determines
intensity, requires ∆x ≈ 1-5 km.
http://storm.aoml.noaa.gov/hwrfxprojects/?projectName=HFIP+Demo+2010
http://www.hfip.org/related_links/
Improvements
• Higher Resolution Models
– A function of Moore’s Law
• Improvements to Initial Model State
– How do you start a model?
– Incorporation of aircraft data (e.g., radar,
dropsondes)
• “Better” Ensembles
– Short range model ensembles for intensity.
– Better “post-processing” of model output.
Useful Tropical Weather Links:
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NHC Pages: Tropical Outlook
Satellite Data: SSEC-UW UKMet-Africa
Blogs: Jeff Masters
Model Comparisons: WxU-Tropical Bob Hart
FloridaWM
Storm Surge Forecasts: NOAA-OPC NOAA
WaveWatch
Storm Surge Observations: CO-OPS
Historical Archive: UW-MKE ESRL Demo
Hurricane Model Descriptions: WUnder NHC