Seasonal Outlook for JJA 2017 for FOCRAII from

Seasonal Outlook for JJA 2017 for FOCRAII from the Met Office’s Glo. Sea 5 System – April initialisation Richard Graham on behalf of GPC Exeter Met Office Hadley Centre Contribution to 13 th session of FOCRAII, 24 -26 April 2017, Beijing, China © Crown copyright Met Office

Introduction • Glo. Sea 5 System run by GPC Exeter • Nino 3. 4 prediction • 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

Glo. Sea 5 Met Office Global Seasonal forecast system 5 Model: Had. GEM 3 GC 2 Resolution: Atmos, N 216 L 85 (~60 km); Ocean: 0. 25° L 75 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/seasonalto-decadal/gpc-outlooks Mac. Lachlan et al. 2014, Scaife et al 2014 © Crown copyright Met

Correlation skills for Nino 3. 4 Glo. Sea 5: http: //www. metoffice. gov. uk/research/climate/seasonal-to-decadal/gpc-outlooks © Crown copyright Met Office

Nino 3. 4 –rainfall teleconnection skills based on El Nino-La Nina composites Glo. Sea 5: http: //www. metoffice. gov. uk/research/climate/seasonal-to-decadal/gpc-outlooks © Crown copyright Met Office

ENSO prediction Nino 3. 4 (from April) Positive Nino 3. 4 anomalies slowly increasing. Range = 0˚C to +1. 5˚C by end of August Glo. Sea 5 © Crown copyright Met Office

forecast skill P(abv) Glo. Sea 5 tercile category probabilities: rainfall JJA Above normal favoured: northern Russia, southwest China, parts of Mongolia, southern Myanmar, Sri Lanka, SW India P(avg) 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 © Crown copyright Met Office P(blw)

skill forecast Glo. Sea 5 outer-quintile category probabilities: rainfall JJA Signals carry through to: >80 th percentile, notably: north and northeast Russia, southwest China, S. Myanmar, Sri Lanka <20 th percentile, weakly: eastern SE Asia mainland, Iran, Afghanistan Little skill evident © Crown copyright Met Office P(>80 th) P(<20 th)

WMO LC-LRFMME deterministic multi-model (9) © Crown copyright Met Office

forecast skill P(abv) Glo. Sea 5 tercile category probabilities: temperature JJA 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 © Crown copyright Met Office P(avg) P(blw)

forecast Glo. Sea 5 outer-quintile category probabilities: temperature JJA Widespread strong signals for >80 th percentile except northern India and parts of SE Asia mainland Skill similar to that for terciles © Crown copyright Met Office skill P(>80 th) P(<20 th)

WMO LC-LRFMME deterministic multi-model (9) © Crown copyright Met Office

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

Glo. Sea 5 tropical storm forecast April-September 2017 Glo. Sea 5 prediction: near normal number of West Pacific storms

Glo. Sea 5 tropical storm forecast April-September 2017: ACE Glo. Sea 5 prediction: slightly lower than normal Accumulated Cyclone Energy (ACE)

Summary: JJA ENSO: • Nino 3. 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 (MJJ): 60%/40% probability for above/below longterm 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