Prognostic Discussion for Long-Lead Hawaiian Outlooks NWS Climate Prediction Center College Park MD 830AM EDT Thu Aug 20 2020 MONTHLY FORECAST DISCUSSION VALID SEPTEMBER 2020 Positive sea surface temperature (SST) anomalies from less than positive one-half degree to near one degree Celsius were observed in the vicinity of the Hawaiian Islands during the last several weeks. For January through July 2020, rainfall total accumulations were: - Lihue Airport 29.09 inches (151 percent of normal) - Honolulu Airport 9.75 inches (117 percent of normal) - Kahului Airport 10.41 Inches (102 percent of normal) - Hilo Airport 70.39 Inches (100 percent of normal) The NCEP Climate Forecast System (CFS) and other climate models of the North American Multi-Model Ensemble (NMME) predict above average SSTs around the Hawaiian Islands through September 2020. This elevates the chances of above normal monthly mean air temperatures for Hawaii in September 2020. Nearly all dynamical models from the NMME suite indicate an increased chance of below normal precipitation over the Hawaiian Islands during September 2020. TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV Hilo A60 76.4 0.5 B60 8.0 9.3 11.0 Kahului A65 79.3 0.4 B60 0.1 0.2 0.5 Honolulu A70 81.8 0.4 B60 0.4 0.6 0.8 Lihue A70 79.4 0.3 B60 1.7 1.9 2.6 SEASONAL FORECAST DISCUSSION VALID SON 2020 - SON 2021 Refer to the prognostic discussion of the long-lead seasonal outlooks for the CONUS and Alaska for a description of the ENSO outlook and other climate conditions relevant to the seasonal outlook, including details on the current state of the atmosphere and ocean. The observed tropical Pacific atmosphere and ocean conditions currently are consistent with ENSO-neutral, with near to below average sea surface temperatures (SSTs) across the central to eastern equatorial Pacific Ocean and above average SSTs in the western equatorial Pacific. Negative subsurface temperature anomalies have strengthened in the east-central Pacific Ocean and negative subsurface temperature anomalies have remained in the far eastern Pacific Ocean. Tropical convection is suppressed over the western and central Pacific. Low-level wind anomalies were easterly in the western and east-central tropical Pacific, and upper-level wind anomalies were westerly over the western and eastern tropical Pacific. The tropical atmosphere and ocean state is consistent overall with ENSO-neutral. A La Nina is likely to develop during Northern Hemisphere autumn 2020 (about 60% chance) and to continue through Northern Hemisphere winter 2020-21, with a probability of about 55 percent. Enhanced probabilities for above normal temperatures are indicated across the Hawaiian Islands in the outlook from SON 2020 to FMA 2021, due to predicted persistence of above normal sea surface temperatures in the NMME dynamical model forecasts through JFM 2021, and supported by statistical models including the Constructed Analog (CA) and Optimum Climate Normals (OCN) through FMA 2021. The signal weakens at longer leads, therefore Equal Chances (EC) for above, near or below normal temperatures are indicated for Hawaii in MAM 2021 and thereafter. The consolidation of dynamical and statistical tools indicates an enhanced likelihood of below normal precipitation in SON 2020 over all Hawaiian Islands. Most dynamical models and a statistical forecast combining the impacts of the ENSO state and decadal trends predicts likely above normal precipitation from NDJ 2020 through FMA 2020, consistent with negative SST anomalies across the eastern equatorial Pacific Ocean and the potential development of La Nina in autumn. Due to considerable uncertainty in the precipitation forecasts among available dynamical and statistical tools over the Hawaiian Islands in MAM 2020 and longer leads, equal chances (EC) for above, near or below normal precipitation are indicated in later seasons. Hilo TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV SON 2020 A60 76.2 0.4 B40 24.3 30.2 40.8 OND 2020 A55 75.5 0.4 EC 28.3 34.5 42.0 NDJ 2020 A55 74.2 0.4 A40 26.4 36.6 43.0 DJF 2021 A50 72.8 0.4 A50 19.6 30.2 33.3 JFM 2021 A45 71.8 0.4 A45 22.0 32.0 44.5 FMA 2021 A40 71.7 0.4 A40 24.6 34.1 45.5 MAM 2021 EC 72.0 0.5 EC 22.5 28.4 34.0 AMJ 2021 EC 72.9 0.5 EC 21.4 23.7 29.0 MJJ 2021 EC 74.0 0.4 EC 20.2 27.5 29.1 JJA 2021 EC 75.2 0.4 EC 19.4 27.2 31.4 JAS 2021 EC 76.1 0.4 EC 25.2 28.6 33.4 ASO 2021 EC 76.4 0.4 EC 26.1 28.8 33.3 SON 2021 EC 76.2 0.4 EC 24.3 30.2 40.8 Kahului TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV SON 2020 A65 79.1 0.4 B40 2.1 3.3 4.8 OND 2020 A60 77.8 0.4 EC 4.2 5.3 8.1 NDJ 2020 A55 75.9 0.4 A40 5.2 7.6 9.5 DJF 2021 A50 73.8 0.4 A50 4.6 6.9 8.7 JFM 2021 A45 72.5 0.4 A45 4.2 6.2 8.2 FMA 2021 A40 72.3 0.4 A40 3.2 4.1 6.4 MAM 2021 EC 73.0 0.4 EC 2.5 3.5 4.6 AMJ 2021 EC 74.3 0.5 EC 1.2 1.6 2.2 MJJ 2021 EC 76.0 0.5 EC 0.7 1.1 1.8 JJA 2021 EC 77.7 0.4 EC 0.7 1.1 1.5 JAS 2021 EC 79.0 0.4 EC 0.8 1.1 1.6 ASO 2021 EC 79.4 0.4 EC 0.8 1.6 2.5 SON 2021 EC 79.1 0.4 EC 2.1 3.3 4.8 Honolulu TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV SON 2020 A65 81.4 0.4 B40 2.5 4.0 5.6 OND 2020 A60 80.0 0.4 EC 4.4 6.4 8.5 NDJ 2020 A55 77.7 0.5 A40 3.9 5.6 8.8 DJF 2021 A50 75.3 0.5 A50 3.7 5.6 8.6 JFM 2021 A45 73.9 0.4 A45 2.1 4.6 7.8 FMA 2021 A40 73.8 0.4 A40 1.9 3.2 4.7 MAM 2021 EC 74.8 0.4 EC 1.8 2.6 3.0 AMJ 2021 EC 76.3 0.4 EC 1.2 1.6 1.8 MJJ 2021 EC 78.2 0.4 EC 0.8 1.4 1.6 JJA 2021 EC 79.9 0.4 EC 0.7 0.8 1.3 JAS 2021 EC 81.3 0.4 EC 1.0 1.4 1.7 ASO 2021 EC 81.7 0.4 EC 1.6 2.4 3.1 SON 2021 EC 81.4 0.4 EC 2.5 4.0 5.6 Lihue TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV SON 2020 A70 79.1 0.3 B40 9.2 10.0 11.2 OND 2020 A65 77.8 0.3 EC 9.2 11.7 15.6 NDJ 2020 A55 75.7 0.3 A40 8.6 12.1 16.9 DJF 2021 A50 73.6 0.4 A50 7.5 8.4 14.0 JFM 2021 A45 72.2 0.4 A45 6.5 8.8 13.8 FMA 2021 A40 72.1 0.5 A40 5.8 8.4 9.9 MAM 2021 EC 72.8 0.5 EC 5.3 6.6 8.0 AMJ 2021 EC 74.2 0.5 EC 4.7 5.5 6.0 MJJ 2021 EC 76.0 0.5 EC 4.9 5.4 5.9 JJA 2021 EC 77.7 0.4 EC 4.4 5.3 6.9 JAS 2021 EC 79.0 0.3 EC 5.3 6.1 7.8 ASO 2021 EC 79.4 0.3 EC 6.2 7.9 8.4 SON 2021 EC 79.1 0.3 EC 9.2 10.0 11.2 FORECASTER: Luke He Anomalies are based on the 1981-2010 means. CLARIFICATION: EC indicated equal chances that the predicted parameter will fall into any one of the three categories, whose boundaries are specific in the tables above. A forecast specification of EC means there is no particulate tilt of the odds toward above normal or below normal conditions in the outlook. For example A40 means a 40% chance that the average temperature or total precipitation will be in the above normal class, B40 means a 40% chance that the average temperature or total precipitation will be in the below normal class, and N35 means a 35% probability that the average temperature or total precipitation will be in the near normal class. When EC is specified, all categories are equally likely. NOTE - These outlooks are intended for use prior to the start of the valid periods. Within any valid period, observations and shorter range forecasts should be consulted. Also, this set of outlooks will be superseded by the issuances of the new set net month, on Thu Sep 17, 2020. $$