Richard Graham on behalf of GPC Exeter Met Office Hadley Centre Seasonal Outlook for JJA 2017 for FOCRAII from the Met Office’s GloSea5 System – April initialisation Richard Graham on behalf of GPC Exeter Met Office Hadley Centre Contribution to 13th session of FOCRAII, 24-26 April 2017, Beijing, China © Crown copyright Met Office

Introduction GloSea5 System run by GPC Exeter ENSO predictions April-initialised precipitation forecasts for JJA and ROC skill April-initialised temperature forecasts for JJA and ROC skill Yangtze river basin forecast Climate Science for Services Partnership (CSSP-China) collaboration Tropical storm frequency – west Pacific Summary © Crown copyright Met Office

GloSea5 Met Office Global Seasonal forecast system 5 Model: HadGEM3 GC2 Resolution: Atmos, N216 L85 (~60km); Ocean: 0.25° L75 Initialisation: Daily, NWP state + NEMOVAR 0.25° Ensembles: Stochastic physics + lagged initialisation Forecasts: 2 per day -> 42 members (over 3 week period) Hindcasts: 7 per 4 times/month -> 28 members, 1993-2015 (23 years) Products: http://www.metoffice.gov.uk/research/climate/seasonal- to-decadal/gpc-outlooks MacLachlan et al. 2014, Scaife et al 2014 © Crown copyright Met Office

ENSO prediction Nino3.4 (from April) Positive Nino3.4 anomalies slowly increasing. Range = 0˚C to +1.5˚C by end of August GloSea5 © Crown copyright Met Office

GloSea5 tercile category probabilities: rainfall JJA forecast skill P(abv) GloSea5 tercile category probabilities: rainfall JJA P(avg) Above normal favoured: northern Russia, southwest China, southern Myanmar, Sri Lanka, SW India Below normal favoured: Iran, Afghanistan, perhaps eastern mainland SE Asia Normal favoured: northwest India, Pakistan Skill is low in most places but some skill Yangtze, SW India, SW China P(blw) © Crown copyright Met Office

GloSea5 outer-quintile category probabilities: rainfall JJA forecast skill GloSea5 outer-quintile category probabilities: rainfall JJA P(>80th) Signals carry through to: >80th percentile, notably: north and northeast Russia, southwest China, S. Myanmar, Sri Lanka <20th percentile, weakly: eastern SE Asia mainland, Iran, Afghanistan Little skill evident P(<20th) © Crown copyright Met Office

GloSea5 tercile category probabilities: temperature JJA forecast skill P(abv) GloSea5 tercile category probabilities: temperature JJA P(avg) Strong signals for above normal all regions except northern Indian subcontinent, and parts of western SE Asia where average also has raised probability Skill mainly limited to SE Asia mainland, parts of India and parts of central and north Asia P(blw) © Crown copyright Met Office

GloSea5 outer-quintile category probabilities: temperature JJA forecast skill GloSea5 outer-quintile category probabilities: temperature JJA P(>80th) P(<20th) Widespread strong signals for >80th percentile except northern India and parts of SE Asia mainland Skill similar to that for terciles © Crown copyright Met Office

June-July-August 2017: rainfall Rainfall and river flow forecast for Yangtze Basin UK-China Climate Science for Service Partnership (CSSP-China) Method: linear regression of GloSea5 ensemble mean hindcasts on: a) observed basin-mean rainfall and b) mean river flow at 5 sites May-June-July 2017 Basin rainfall: 60% chance of above-average 40% chance of below-average River flow: 55% chance of above-average 45% chance of below-average Illustrative bar plot and cor maps illustrative ts, Rel & ROC plots (good skill) illustrative ts, Rel & ROC plots (bad skill) Met Office, CMA, IAP collaboration: Philip Bett, Adam Scaife, Chaofan Li, Chris Hewitt, Nicola Golding, Peiqun Zhang, Nick Dunstone, Doug Smith, Hazel E. Thornton. June-July-August 2017: rainfall

GloSea5 tropical storm forecast April-September 2016 GloSea5 prediction for fewer West Pacific storms than usual

GloSea5 tropical storm forecast April-September 2017 GloSea5 prediction: near normal number of West Pacific storms

GloSea5 tropical storm forecast April-September 2017: ACE GloSea5 prediction: slightly lower than normal Accumulated Cyclone Energy (ACE)

Summary ENSO: Nino3.4: positive SST anomalies slowly increasing spread = 0˚C to +1.5˚C by end of August Rainfall: Above normal: strongest signals for northern Russia, southwest China, southern Myanmar, Sri Lanka, SW India Below normal: strongest signals Iran, Afghanistan, perhaps eastern mainland SE Asia. Skill is generally low apart from some favoured regions Yangtze Basin: 60%/40% probability for above/below long-term mean (note: 2 category, not tercile) Temperature: Strong signals for above normal all regions except northern Indian subcontinent and Western mainland SE Asia West Pacific tropical storms: near normal numbers indicated © Crown copyright Met Office

Thank you! © Crown copyright Met Office