Seasonal Forecast for Summer 2013 for Hong Kong

9 Apr 2013, FOCRAII, BeijingH 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 2012Actual Forecast

Temp. Above Normal Normal to above normal

Rainfall Below normal Normal to above normal X

Review of 2012 JJA forecast

Temperature (C) Rainfall (mm)Obs. Normal

Range(81-10)

Obs. Normal Range(81-10)

Jun 12 28.1 27.6-28.2

261.5 315-597

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 – CFSv2 & JMA-CGCM vs actual MSLP

CFSv2

Actual

JMA-CGCM

Methodology El Niño/La Nina considerationLarge-scale circulation pattern forecast by major

centers (CFSv2, JMA-CGCM, ECMWF)Forecasts from major centers Statistical downscaling (from NCEP CFSv2)

Simple regressionPrinciple component regression

ENSO Status

8

Neutral in JJA

Large-scale circulation pattern

500Z (upper) & MSLP (lower) Jun 2013

10

NCEP JMA ECMWF(non-normalized)

850 Wind (upper) & Temp (lower) Jun 2013

11

NCEP JMA ECMWF (non-normalized)

500Z (upper) & MSLP (lower) Jul 2013

12

NCEP JMA ECMWF(non-normalized)

850 Wind (upper) & Temp (lower) Jul 2013

13

NCEP JMA ECMWF (non-normalized)

500Z (upper) & MSLP (lower) Aug 2013

14

NCEP JMA ECMWF(non-normalized)

850 Wind (upper) & Temp (lower) Aug 2013

15

NCEP JMA ECMWF (non-normalized)

Short summaryJun Jul Aug

NCEP NE’lies Low over E of Luzon

NE’liesLow over NE Luzon

W’liesLow over Eastern China

JMA E’liesLow over Luzon

Ridge E’iesTrough over centralSCS

EC Ridge Ridge Ridge

Above normal temperature ?Below normal rainfall ?

Statistical downscalingTemp. Normal SD Mean pB pN pAJun 27.9 28.1 0.13 0.46 0.41Jul 28.8 28.8 0.25 0.44 0.31Aug 28.6 28.7 0.22 0.38 0.40JJA 28.6 28.4 0.13 0.34 0.53

Rainfall Normal SD Mean pB pN pAJun 456 354 0.49 0.41 0.10Jul 376 320 0.41 0.45 0.14Aug 432 388 0.39 0.43 0.18JJA 1265 1198 0.29 0.56 0.15

Normal to warm

Normal to dry

18

JJA temperature forecasts from major centers

2013

for ref only Cool Norm Warm

IRI 0.25 0.35 0.40

JAMSTEC 0.30 0.35 0.35

NCEP Conditional prob (|AN) 0.11 0.33 0.56

JMA Conditional prob (|AN) 0.20 0.33 0.47

Average 0.22 0.34 0.45

2013

Cool Norm Warm

CMA/BCC 0.4 0.3 0.3

NOAA/CPC 0.3 0.3 0.4

ECMWF 0.05 0.3 0.65

JMA 0.25 0.34 0.41

UKMO 0.1 0.45 0.45

NCEP Stat. Downscaling 0.13 0.34 0.53

Average 0.21 0.34 0.46

JJA

Normal to above normal

19

JJA rainfall forecasts from major centers

19

2013

for ref only Dry Norm Wet

IRI 0.33 0.33 0.33

APCC 0.33 0.33 0.33

JAMSTEC 0.35 0.35 0.30

NCEP Conditional prob (|AN) 0.13 0.74 0.13

JMA Conditional prob (|BN) 0.10 0.70 0.20

Average 0.25 0.49 0.26

2013

Dry Norm Wet

CMA/BCC 0.3 0.35 0.35

NOAA/CPC 0.35 0.35 0.3

ECMWF 0.4 0.3 0.3

JMA 0.33 0.33 0.33

UKMO 0.33 0.33 0.33

NCEP Stat. Downscaling 0.29 0.56 0.15

Average 0.33 0.37 0.29

JJA

Normal to dry

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

HK

21Normal

Statistical downscalingNormal SD mean

No. of TC in JJA 3.2 2.7

2-3 TC in JJA, near normal

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

Thanks

25

ECMWF

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