Prognostic Discussion for Long-Lead Hawaiian Outlooks NWS Climate Prediction Center College Park MD 830AM EDT Thu Sep 17 2020 MONTHLY FORECAST DISCUSSION VALID OCTOBER 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 August 2020, rainfall total accumulations were: - Lihue Airport 30.37 inches (142 percent of normal) - Honolulu Airport 9.88 inches (111 percent of normal) - Kahului Airport 10.44 Inches (98 percent of normal) - Hilo Airport 74.64 Inches (93 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 October 2020. This elevates the chances of above normal monthly mean air temperatures for Hawaii in October 2020. Nearly all dynamical models from the NMME suite indicate an increased chance of below normal precipitation over the Hawaiian Islands during October 2020. TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV Hilo A60 75.7 0.5 B40 7.8 8.6 12.1 Kahului A65 78.2 0.4 B40 0.3 0.6 1.1 Honolulu A70 80.2 0.5 B40 0.5 1.3 1.9 Lihue A70 78.1 0.3 B40 2.5 3.3 4.2 SEASONAL FORECAST DISCUSSION VALID OND 2020 - OND 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 La Nina, with below average sea surface temperatures (SSTs) across the east-central and the 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 positive subsurface temperature anomalies have strengthened in the western Pacific Ocean. Tropical convection is suppressed over the western and central Pacific. Low-level and upper-level wind anomalies were near average over most of the tropical Pacific. The tropical atmosphere and ocean state is consistent overall with La Nina. La Nina conditions are likely to continue through Northern Hemisphere winter 2020-21, with a probability of about 75 percent. Enhanced probabilities for above normal temperatures are indicated across the Hawaiian Islands in the outlook from OND 2020 to MAM 2021, due to predicted persistence of above normal sea surface temperatures in the NMME dynamical model forecasts through FMA 2021, and supported by statistical models including the Constructed Analog (CA) and Optimum Climate Normals (OCN) through MAM 2021. The signal weakens at longer leads, therefore Equal Chances (EC) for above, near or below normal temperatures are indicated for Hawaii in AMJ 2021 and thereafter. Most dynamical models and a statistical forecast combining the impacts of the ENSO state and decadal trends predict likely above normal precipitation from NDJ 2020 through MAM 2021, consistent with negative SST anomalies across the eastern equatorial Pacific Ocean and continuing La Nina conditions through the winter. Due to considerable uncertainty in the precipitation forecasts among available dynamical and statistical tools over the Hawaiian Islands in OND 2020, and in AMJ 2021 and longer leads, equal chances (EC) for above, near or below normal precipitation are indicated in these seasons. Hilo TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV OND 2020 A60 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 A55 72.8 0.4 A50 19.6 30.2 33.3 JFM 2021 A50 71.8 0.4 A60 22.0 32.0 44.5 FMA 2021 A45 71.7 0.4 A50 24.6 34.1 45.5 MAM 2021 A40 72.0 0.5 A40 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 OND 2021 EC 75.5 0.4 EC 28.3 34.5 42.0 Kahului TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV OND 2020 A65 77.8 0.4 EC 4.2 5.3 8.1 NDJ 2020 A60 75.9 0.4 A40 5.2 7.6 9.5 DJF 2021 A55 73.8 0.4 A50 4.6 6.9 8.7 JFM 2021 A50 72.5 0.4 A60 4.2 6.2 8.2 FMA 2021 A45 72.3 0.4 A50 3.2 4.1 6.4 MAM 2021 A40 73.0 0.4 A40 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 OND 2021 EC 77.8 0.4 EC 4.2 5.3 8.1 Honolulu TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV OND 2020 A65 80.0 0.4 EC 4.4 6.4 8.5 NDJ 2020 A60 77.7 0.5 A40 3.9 5.6 8.8 DJF 2021 A55 75.3 0.5 A50 3.7 5.6 8.6 JFM 2021 A50 73.9 0.4 A60 2.1 4.6 7.8 FMA 2021 A45 73.8 0.4 A50 1.9 3.2 4.7 MAM 2021 A40 74.8 0.4 A40 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 OND 2021 EC 80.0 0.4 EC 4.4 6.4 8.5 Lihue TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV OND 2020 A70 77.8 0.3 EC 9.2 11.7 15.6 NDJ 2020 A65 75.7 0.3 A40 8.6 12.1 16.9 DJF 2021 A55 73.6 0.4 A50 7.5 8.4 14.0 JFM 2021 A50 72.2 0.4 A60 6.5 8.8 13.8 FMA 2021 A45 72.1 0.5 A50 5.8 8.4 9.9 MAM 2021 A40 72.8 0.5 A40 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 OND 2021 EC 77.8 0.3 EC 9.2 11.7 15.6 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 Oct 15, 2020. $$