Assessment (as of 29 May 2018):
- Sea surface temperatures of the central and eastern equatorial Pacific returned to normal in April 2018. Based on the latest oceanic observations as well as forecasts by a number of climate models around the world, sea surface temperature of the region is expected to remain normal this summer. As such, the effects it has on Hong Kong's summer temperature and rainfall are unlikely to be significant.
- Climate models around the world generally forecast that the southerly winds over the coast of southern China would be weaker than normal this summer, and hence less moisture transport to the region. Under this situation, summer rainfall in Hong Kong in 2018 is likely to be normal to below normal.
- Under the influence of global warming and local urbanization, summer temperatures in Hong Kong exhibit a significant long-term rising trend. The chance of normal to above-normal temperature is generally higher. This temperature trend is in line with the summer temperature forecast for southern China given by climate models around the world. In addition, with normal to below-normal summer rainfall anticipated in Hong Kong, the cooling effect due to precipitation will also be less prominent.
- 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 2018 (September to November 2018) will be available around 1st September 2018.
Seasonal forecast charts provided by G-RCM and major climate centres: