1. Seasonal Forecast for Summer 2013 for Hong Kong
9 Apr 2013, FOCRAII, Beijing
H W Tong
Hong Kong Observatory

2. Seasonal Forecast at HKO
Temperature and rainfall
Most (or two most) likely category
No. of TC entering the 500 km range of Hong Kong (for internal use only)

3. Verification- JJA 2012 Actual Forecast Temp. Above Normal
Normal to above normal 
Rainfall
Below normal
Normal to above normal X

4. However, Aug 2012 was expectedly dry
Review of 2012 JJA forecast
Temperature (C)
Rainfall (mm)
Obs.
Normal Range
(81-10)
Jun 12
28.1
261.5
Jul 12
28.8
467.8
Aug 12
29.5
127.0
JJA 12
856.3
Jun 2012 was well forecast
However, Aug 2012 was expectedly dry

5. August 2012

6. Aug 2012 – CFSv2 & JMA-CGCM vs actual MSLP

7. Methodology El Niño/La Nina consideration
Large-scale circulation pattern forecast by major centers (CFSv2, JMA-CGCM, ECMWF)
Forecasts from major centers
Statistical downscaling (from NCEP CFSv2)
Simple regression
Principle component regression

8. ENSO Status
Neutral in JJA

9. Large-scale circulation pattern

10. 500Z (upper) & MSLP (lower)  Jun 2013
NCEP
JMA
ECMWF (non-normalized)

11. 850 Wind (upper) & Temp (lower)  Jun 2013
NCEP
JMA
ECMWF (non-normalized)

12. 500Z (upper) & MSLP (lower)  Jul 2013
NCEP
JMA
ECMWF (non-normalized)

13. 850 Wind (upper) & Temp (lower)  Jul 2013
NCEP
JMA
ECMWF (non-normalized)

14. 500Z (upper) & MSLP (lower)  Aug 2013
NCEP
JMA
ECMWF (non-normalized)

15. 850 Wind (upper) & Temp (lower)  Aug 2013
NCEP
JMA
ECMWF (non-normalized)

16. Above normal temperature ?
Short summary
Jun
Jul
Aug
NCEP
NE’lies
Low over E of Luzon
Low over NE Luzon
W’lies
Low over Eastern China
JMA
E’lies
Low over Luzon
Ridge
E’ies
Trough over central
SCS EC
Above normal temperature ?
Below normal rainfall ?

17. Statistical downscaling
Temp.
Normal
SD Mean pB pN pA
Jun
27.9
28.1
0.13
0.46
0.41
Jul
28.8
0.25
0.44
0.31
Aug
28.6
28.7
0.22
0.38
0.40
JJA
28.4
0.34
0.53
Normal to warm
Rainfall
Normal
SD Mean pB pN pA
Jun
456
354
0.49
0.41
0.10
Jul
376
320
0.45
0.14
Aug
432
388
0.39
0.43
0.18
JJA
1265
1198
0.29
0.56
0.15
Normal to dry

18. JJA temperature forecasts from major centers
Normal to above normal

19. JJA rainfall forecasts from major centers
Normal to dry 19

20. Number of tropical cyclones entering the 500 km range of Hong KongHK

21. Normal 21

22. Statistical downscaling
Normal
SD mean
No. of TC in JJA
3.2
2.7
2-3 TC in JJA, near normal

23. Preliminary summer forecast for Hong Kong 2013
Temperature
Normal to above normal
Rainfall
Normal to below normal
No. of TC entering 500 km of Hong Kong
2-3

24. Thanks

25. ECMWF 25

26. No of TC in El Nino/La Nina/Neutral years