1. A Few Words on Hurricane Forecasts

2. 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.

3. Intensity Error Intensity Forecasts are still in need of improvement:
Rule of Thumb:
Error ± 10 kts

4. What’s With All the Models?

5. 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

6. Forecast Track Skill in 2012 (Atlantic Basin)
The Best:
FSU Super Ensemble
NHC Official Forecast
GFS Ensembles
ECMWF Ensembles
GFS
ECMWF

7. 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.

8. GFS Ensemble Forecasts for Sandy (72 hours before landfall)

9. ECMWF Ensemble Forecast for Sandy (72 hours before landfall)

10. 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.

11. 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.

12. Latest Developments

13. Inner core dynamics, which determines intensity, requires ∆x ≈ 1-5 km.
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 ≈ km.
Inner core dynamics, which determines intensity, requires ∆x ≈ 1-5 km.

14. Higher Resolution Models Improvements to Initial Model State
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.

15. Useful Tropical Weather Links:
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