Application%20of%20T382%20CFS%20Forecasts%20for%20Dynamic%20Hurricane%20Season%20Prediction

1
Application of T382 CFS Forecasts for Dynamic
Hurricane Season Prediction

• J. Schemm, L. Long, S. Saha and
• S. Moorthi
• NOAA/NWS/NCEP
• October 21, 2008
• The 33rd Climate Diagnostics and Prediction
  Workshop, Lincoln, NE

2
Outline

• Description of the CFS experiment
• Datasets Used
• IRI Detection and Tracking Method
• Analysis of storm activity statistics
• Focus on the Atlantic Basin
• Statistics
• A look at CFS predictions for 2008
• Future plan

3
CFS T382 hurricane season experiments

• One of the FY07/08 CTB internal projects
• AGCM - 2007 operational NCEP GFS in T382/L64
  resolution
• LSM - Noah LSM
• OGCM - GFDL MOM3
• 3. All runs initialized with NCEP/DOE R2 and
  NCEP GODAS.
• Initial conditions at 0Z, Apr. 19, 20, (21) and
  May 15(FY07)
• for 1981-2007. Forecasts extended to December
  1.
• 4. For May 15 cases, runs in T62 and T126
  resolutions also performed.

4
Datasets

• CFS hindcasts at T382
• May 15th Initial Condition
• Output at every 3 hours
• 1981-2007, 27 years
• April 19th and April 20th Initial Condition
• Output at every 6 hours
• 1981-2008, 28 years
• More appropriate ICs for CPC Operational
  Hurricane Season Outlook
• Observations from the HURDAT and JTWC Best Track
  Dataset
• -Tropical depressions and subtropical storms
• are not included in storm counts.

5
Tropical Cyclone Detection Method

• Based on method devised by Camargo and Zebiak
  (2002) at IRI
• Detection algorithm uses basin-dependent
  threshold criteria for three variables
• Vorticity, xthresh
• xthresh 2sx
• 10-m Wind Speed, uthresh
• uthresh ugl su ugl wind speed
  averaged over
• 
  all global basins
• Vertically integrated temp anomaly, Tthresh
• Tthresh sT/2
• Calculated using only warm-core systems

6
Eight conditions must be met for a point to be
considered a tropical cyclone

• 1. 850-hPa relative vorticity gt xthresh
• 2. Maximum 10-m wind speed in a 7x7 box gt uthresh
• 3. SLP is the minimum in the centered 7x7 box
• 4. Temp anomaly averaged over the 7x7 box and
  three pressure levels (300, 500, 700 mb) gt
  Tthresh
• 5. Temperature anomaly averaged over the 7x7 box
  is positive at all levels (300, 500, 700 mb)
• 6. Temperature anomaly averaged over the 7x7 box
  at 300mb gt 850mb
• 7. Wind speed averaged over the 7x7 box at 850mb
  gt 300mb
• 8. The storm must last for at least 6 hours.
• Criteria 5 6 define a warm core
  system.

7
Storm Tracking

• Once a point is designated as a tropical cyclone,
  the cyclone is tracked forward and backward in
  time to create a full storm track.
• The maximum vorticity in a 5x5 grid around the
  cyclone is found and a new 3x3 box is formed
  around it.
• At the next time step, if the maximum vorticity
  in this new box is greater than 3.5 x 10-5 s-1,
  the procedure is repeated.
• This point has become part of the storm track.
• If two storm tracks are the same, they are
  considered the same cyclone and counted as one.

8
Four NH Ocean Basins
9
Examples of Storm Tracks for 4 NH Basins
10
Atlantic Basin
Atlantic Tropical Storms
11
Eastern Pacific Basin
Eastern Pacific Tropical Storms
12
JJA Nino 3.4 SST Index
13
JJA Atlantic MDR SST Index
14
Tropical Storm Origins, 1981-2007 ASO
OBS
IC0515
IC0419
IC0420
15
Atlantic Basin Correlations
Anomalies of Atlantic Storms
N27 N13 N13 N8
N5 N14
0.79
Red Statistically Significant at 0.95
Correlations based on 27-year anomaly
16
0.90
Red Statistically Significant at 0.95
17
2008 Atlantic Season Summary
Obs NOAA Outlook Outlook Update CFS-Stat May CFS-Stat Update
Named Storm 15 12-16 14-18 9-16 13-16
Hurricane 7 6-9 7-10 5-9 7-10
Major Hurricane 4 2-5 3-6 2-4 3-5
As of October 17, 2008
18
Atlantic Basin Prediction for 2008

• Two additional runs were made using July 15th and
  16th initial conditions for 2008 only
• Used as a trial run for the CPC Hurricane Outlook
  Update

19
Atlantic BasinCFS 2008 Monthly Storm Count
3
20
2008 Atlantic Storm Tracks
(Courtesy of Unisys)
Large number of storms over the Gulf of Mexico
this year
21
Resemble Bertha and Cristobal
22

• .Summary
• CFS in T382 resolution exhibits robust
  climatological
• seasonal cycle of tropical cyclone over four
  NH basins.
• Warming trend and intensification of hurricane
  activity in
• the Atlantic basin captured in the CFS
  hindcasts.
• Fair level of skill in predicting interannual
  variability of seasonal
• storm activities based on the limited number
  of forecast runs.
• Continue to increase number of ensemble members
  for better
• climatology and storm statistics. Hope to
  provide input for 2009
• Hurricane Season Outlook with real time
  prediction runs.
• Prospect of multi-model ensemble approach for
  dynamical
• hurricane season prediction