Dry Season Forecast: Weak La Nina Favors Above Normal Temperatures, Below Normal Precipitation
By National Weather Service • Melbourne, Florida // October 18, 2017
National Weather Service in Melbourne
NATIONAL WEATHER SERVICE • MELBOURNE, FLORIDA – The National Weather Service’s 2017-2018 Dry Season forecast for East Central Florida calls for a potential weak La Nina, favoring above normal temperatures and below normal precipitation.
Cooler than average sea surface temperatures in the eastern equatorial Pacific Ocean are expected to lead to weak La Nina-conditions during the fall and winter.
Seasonal temperatures are expected to trend above normal, though considerable week-to-week and month-to-month variability is expected as other large scale weather patterns normally overwhelm a weak ENSO signal.
Forecast Basis & Interpretation
The seasonal forecast is produced by a team of National Weather Service Melbourne meteorologists that employ the use of linear and logistic regression equations as well as analog-based techniques.
These methods are based on the official observed and forecast Niño 3.4 and 3.0 values from the CPC and historical weather data for the Central Florida region. The accuracy of these indices will have a bearing on the accuracy of the seasonal forecast.
The Florida dry season forecast is issued for the period between November 1, 2017 and April 30, 2018 and is intended to serve as an early warning of significant impacts from climatic variability for planners and decision makers.
TEMPERATURES: The forecast the 2017-2018 dry season slightly favors above normal temperatures, based on guidance from CPC and the development of weak La Nina conditions during fall and winter.
Local research suggests a smaller “warm” signal at the beginning of the season with greater chances of above normal temperatures occurring from February through April.
While temperatures over both three-month periods are forecast to trend above normal, significant week-to-week and month-to-month variation is expected as other large scale weather patterns often overwhelm a weak La Nina.
PRECIPITATION: The forecast for the 2017 – 2018 dry season favors below average precipitation, based on guidance from CPC and the assumption of continued cool ENSO conditions through fall and winter. Logistic regression and analog-based techniques support greater chances (50 – 55%) of drier than normal conditions occurring during the entire dry season.
This is in line with the latest CPC forecast which also favors below normal precipitation. Drier than usual conditions during this time of year, when only about 1/3 of the area’s annual rainfall occurs, would promote drought and condition the environment for an active wildfire season into the spring of 2018.
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