1. Man-sze, CHEUNG Hong Kong Observatory
Seasonal Forecast for Summer 2017 for Hong Kong and the Latest Development in Extended Range Forecast
Man-sze, CHEUNG
Hong Kong Observatory

2. Outline Review of seasonal forecast for JJA in 2016
Annual number of tropical cyclones entering the 500 km range of Hong Kong
Extended range forecast products for the general public

3. Review of JJA in 2016 Temperature Normal to above normal Above Normal
Forecast
Actual
Temperature
Normal to
above normal
Above Normal
(29.2 °C)
Rainfall
Near Normal
Normal
(1056 mm)
TC(N500)
2-3 3
TC in 500 km
Mirinae (Jul)
Nida (Jul)
Dianmu (Aug)

4. Seasonal Forecast for Hong Kong JJA 2017

5. ENSO Status
The central and eastern equatorial Pacific is expected to continue to warm through spring and summer 2017 with increasing chance of El Niño development.
3.1.3SST Weekly / Monthly maps ,

6. ENSO Status Seasons (2017) AMJ MJJ JJA JAS ASO SON OND
Assorted plot
Seasons (2017)
AMJ
MJJ
JJA
JAS
ASO
SON
OND
Avg. of all models
0.4
0.6
0.7
0.8
0.9
0.5

7. Tercile category statistics in El Niño's and ENSO neutral year
Most likely categories:
Temperature in JJA
Normal to
above normal
(global warming)
Rainfall in JJA
Normal to below normal
(El Niño years)
Uncertain
(ENSO neutral years)

8. Tercile Probabilities Summary
Forecast category of JJA 2017 from different centres
Centres
Temperature
Rainfall
CMA/BCC
N to AN
N to BN
ECMWF(MJJ)
JMA
No signal
UKMO
NOAA/CPC
Normal
APCC (JAS)
WMO LC (MJJ)
Normal to Cool/Warm/Dry/Wet = N -
* N – Warm/Cool/Wet/Dry : Normal to Warm/Cool/Wet/Dry

9. Consensus categorical forecast by pre-season indices

10. Selected predictors Ji: 1000 hPa V over 10-30N, 115-130E
DJF UMI
DJF Ji index
DJF SST index (SSTa-SSTb)
SSTa
SSTb
Ji: 1000 hPa V over 10-30N, E
UMI: 1000 hPa V over N, E

11. 30-year running correlation with JJA rainfall

12. Performance of pre-season indices
JJA rainfall
Random
forecast
Persistent NA
Persistent NB
Consensus of pre-season predictors
~25 26 30
~11 12 13
14 *
2017 JJA Rainfall : Normal to Above Normal
* Miss a dry summer (2002) and a wet summer (2008)

13. Seasonal Climate Forecast
ENSO Consideration:
JJA
FC Cat
Temp.
N to AN
Rainfall
N to BN
Normal to warm
Normal to dry
Consensus of major centres:
JJA
FC Cat
Temp.
N to AN
Rainfall
N to BN
Normal to warm
Normal to dry
Forecasts from pre-season indices
JJA
FC Cat
Rainfall
N to AN
Normal to wet
June - August 2017
Temperature: Normal to above normal
Rainfall: Near normal

14. New method to forecast annual N500

15. Predictors
Nino 3.4 sst
500 hPa zonal wind ( N, E)

16. obs and reanalysis

17. Workflow Training data: 1981/1982 – 1996 +
Apply Poisson regression, qq mapping, std anomaly mapping to generate quantitative forecast
Get average from the three forecasts
Construct a forecast range covering 4 consecutive integers (e.g. mean = 4.x, f/c range = “3-6”, nearest 4 consecutive integers) 2 3 4 5 6 7
Training data: 1981/1982 –
Verification data:
Reference forecast: mode of bin (width=4) in prevailing climatology

18. Climatology of N500

19. Available Model Data ECMWF: NCEP:
Forecast up to Sep (initialized on 1 Mar)
NCEP:
Forecast up to Nov (initialized in late Feb)

20. Verification results (1997-2016)
Predictor
No. of correct forecasts
RMSE
Climate 12
0.49
NCEP U500 + EC N34 (qq,sam,poi) 15
0.47
N500 Forecast for 2017 : 5.0 (4-7)

21. Annual outlook issued in March

22. Seamless forecast – are we ready?
Climate projection
Seasonal forecast
2-hour RF nowcast
9-day forecast

23. Extended outlook forecast
Tmin temperature forecast in October – March
Day 10 – 28
Calibration using qq mapping and standardized anomaly mapping
Verification period; 2013/ /16 for day 10-14; 2011/12 – 2015/16 for day 15-28
Calibrated forecasts are skillful
We are developing graphical products for general public

24. Thank You
And we welcome: To share our experience; To cooperate in meteorological technologies and equipment; and To share our data