Seasonal Forecast for Summer 2013 for Hong Kong

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

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)

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

Review of 2012 JJA forecast Temperature (C) Rainfall (mm) Obs. 261. 5 Normal Range (81 -10) 315 -597 Jun 12 28. 1 Normal Range (81 -10) 27. 6 -28. 2 Jul 12 28. 8 28. 6 -29. 0 467. 8 262 -490 Aug 12 29. 5 28. 3 -28. 8 127. 0 301 -564 JJA 12 28. 8 28. 3 -28. 6 856. 3 1021 -1509 Jun 2012 was well forecast However, Aug 2012 was expectedly dry

August 2012

Aug 2012 – CFSv 2 & JMA-CGCM vs actual MSLP JMACGCM CFSv 2 Actual

Methodology El Niño/La Nina consideration Large-scale circulation pattern forecast by major centers (CFSv 2, JMA-CGCM, ECMWF) Forecasts from major centers Statistical downscaling (from NCEP CFSv 2) Simple regression Principle component regression

ENSO Status Neutral in JJA 8

Large-scale circulation pattern

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

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

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

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

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

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

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

Statistical downscaling Temp. Normal SD Mean p. B p. N p. A 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. 6 28. 4 0. 13 0. 34 0. 53 Normal to warm Rainfall Normal SD Mean p. B p. N p. A Jun 456 354 0. 49 0. 41 0. 10 Jul 376 320 0. 41 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

JJA temperature forecasts from major centers Normal to above normal 18

JJA rainfall forecasts from major centers Normal to dry 19 19

Number of tropical cyclones entering the 500 km range of Hong Kong HK

Normal 21

Statistical downscaling No. of TC in JJA Normal SD mean 3. 2 2. 7 2 -3 TC in JJA, near normal

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

Thanks

ECMWF 25

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