Assessment (as of 31 May 2017):
- Sea surface temperatures over the eastern equatorial Pacific remained warmer than normal in the past month. According to forecasts by a number of climate models around the world, the central to eastern equatorial Pacific is likely to warm up in the next few months with increasing chance of El Niño development. If El Niño occurs in summer, there is generally higher chance for Hong Kong to experience normal to below-normal summer rainfall.
- Under the influence of global warming and local urbanization, summer temperatures in Hong Kong exhibit a significant long-term rising trend. Climate models around the world forecast normal to above-normal temperature over southern China for this summer.
- Climate models around the world do not clearly indicate any trend for summer rainfall over southern China in 2017. Statistical forecasts given by pre-season indices of atmospheric circulation and sea surface temperature indicate a higher chance for normal to below-normal summer rainfall in Hong Kong. Taking the above information and the chance of El Niño development into consideration, the summer rainfall in Hong Kong is expected to be normal to below normal.
- Climate prediction centres around the world generate seasonal forecasts, employing a variety of methods including
dynamical models, statistical methods, expert judgment and combinations of them. Predictions from different centres do
not always agree and large discrepancies can occur at times. The Observatory adopts an ensemble approach to formulate
its seasonal forecast for Hong Kong, taking into consideration available products from major climate prediction centres
and the Global-Regional Climate Model (G-RCM) operated in-house. Thus,
the resulting forecast issued by the Observatory may be different from the forecast given by G-RCM.
- The Observatory gratefully acknowledges the Tokyo Climate Center of the Japan Meteorological Agency and the National
Centers for Environmental Prediction of National Oceanic and Atmospheric Administration, USA for providing dynamical
prediction model forecast and hindcast data to support the formulation of seasonal forecast for Hong Kong.
- Forecast for autumn 2017 (September to November 2017) will be available around 1st September 2017.
Seasonal forecast charts provided by G-RCM and major climate centres: