Seasonal prediction of South Asian summer monsoon 2010: Met Office Michael Vellinga and many colleagues at the Met Office Hadley Centre and ECMWF

Probabilistic seasonal forecasts with dynamical models Nino 3.4 forecasts Forecast probabilities for South Asian region for: JJA rainfall sea surface air temperature AMJ surface air temperature Results from: Met Office’s GloSea4 system: anomalies relative to 1989-2002 hindcasts ECMWF’s System3: anoms. relative to 1981-2005

Nino3.4

GloSea4: Nino3.4 Jan f/c

GloSea4 Nino3.4: Feb f/c

GloSea4 Nino3.4: March f/c

ECMWF: Nino3.4 Jan f/c

ECMWF Nino3.4: Feb f/c

ECMWF Nino3.4: March f/c

Nino3.4 March f/c

June-July-August Precipitation

Precipitation June-July-August normal or above-normal rainfall more likely, below normal less likely for most of region Opposite signal SE of the region (Myanmar/Thailand/Indochina) All categories equally likely over most of Pakistan

Precipitation GloSea4 ROC scores June-July-August Limited skill of Glosea4 for Asian summer monsoon rainfall tercile anomalies months 4-6

ECMWF JJA precipitation Above average rainfall: ECMWF JJA precipitation ‘wet signal’ (above-average precipitation more likely, and below-average precipitation less likely) similar as GloSea4 less restricted to north, south and west of region and over Himalayas equal probabilities for all categories for C India Average rainfall: Below average rainfall

Forecasts for June (from MAJ forecasts from WMO-LCMME)

April-May-June temperature

Temperature most of region: Increased probability of warmer than normal, reduced probability of colder than normal. Increased probability of well-above normal temperature

Temperature

Temperature ECMWF Similar as GloSea4, but weaker signal for central and eastern India, Bangladesh

JJA 2m temperature No clear signal for most of region For NE India, Bangladesh, Himalayas: Increased probability of above-normal temperatures, reduced probability of below-normal temperatures

June-July-August SST

Sea surface temperature Indian Ocean: Increased probabilities of above-average SST in, reduced probability of normal or below-normal SST in E Pacific: Increased probabilities of normal to below-normal SST, reduced probability of above-normal SST

Summary: based on GloSea4 seasonal forecasts Indications that ENSO/Nino3.4 SST will move from current warm phase to neutral or La Nina phase by June 2010 Warm SST in Indian Ocean June-July-August more likely Increased probability for normal to above-normal precipitation in June-July-August for most of S Asia. Regional variations! Increased probability for normal to warmer than normal temperatures in May-April-June for most of region Lasting into June-July-August for NE and Maldives for, no clear signal elsewhere)

the end

Ensemble-mean SST anomalies