National Weather Service United States Department of Commerce

 

The heat and humidity of summer is finally coming to an end.  September is the beginning of meteorological fall -- a transition season when falling sun angles and shorter days cause temperatures to drop.  Cold fronts bringing cooler and drier air from Canada will become more common as fall progresses.  High temperatures normally in the 80s in September fall into the mid 60s by the end of November.  Fall is also when most locations across the eastern Carolinas will experience their first frost and freezing temperatures of the season.

     How is meteorological fall different from fall on the calendar?

 

The NWS Climate Prediction Center is predicting an enhanced potential (40 to 50 percent) for above normal temperatures across the Carolinas this fall.  There are no clear predictive signals concerning precipitation, so the outlook is for "equal chances" of below, near, or above normal rainfall amounts.

Fall 2022 CPC temperature outlook

Fall 2022 temperature outlook from the Climate Prediction Center

Fall 2022 precipitation outlook from the Climate Prediction Center

Fall 2022 precipitation outlook from the Climate Prediction Center

 

Temperatures

Factors that will affect temperatures across the Carolinas this fall include:

  • Ongoing trends toward warmer air temperatures as a consequence of Climate Change
  • Sea surface temperatures 2° to 9° F above normal across a large portion of the North Atlantic Ocean
  • A continuing La Niña oceanic and atmospheric pattern

Recent Climate Change is being caused by increasing atmospheric concentration of greenhouse gases such as carbon dioxide and methane from the burning of fossil fuels and the clearing of land.  These gases trap heat within the atmosphere that would otherwise radiate out into space.  Average temperatures across the eastern Carolinas have increased by just over 1° F since record-keeping began, less than the nearly 2° F average increase for the planet as a whole.

     Climate.gov: How have global temperatures changed?

     NC Climate Office: Climate Change in North Carolina

 

Sea Surface Temperature anomalies as of September 2, 2022.  Most of the North Atlantic north of the subtropics is very warm relative to normal

Also of concern is a large region of above-normal sea surface temperatures across much of the North Atlantic ocean north of the tropics.  (See graphic at right)  Between the Carolinas and Bermuda water temperatures are around 1° C (1.8° F) above normal.  But near the Canadian maritime provinces sea water temperatures are nearly 5° C (9° F) above normal.  Air moving south from Atlantic Canada over the next several months will pick up extra heat as it travels across this warm ocean surface, possibly affecting East Coast temperatures into the coming winter too.

 

La Nina, a natural periodic cooling of ocean waters across the tropical Pacific ocean, causes shifts in the weather across large portions of the planet.  Across the Carolinas, La Niña is associated with a tendency toward above-normal temperatures during most of the year including the fall months.  The jet stream shifts northward across the North American continent during La Niña, making it less likely that cold Canadian airmasses will move south.

     What are El Niño and La Niña and how do they affect the weather?

 

The following table shows how September through November temperatures compared to normal during each of the La Niña fall seasons over the past 20 years at four local cities.

  Wilmington Lumberton N. Myrtle Beach Florence
1991-2020 AVERAGE FALL TEMPERATURE 65.6° 63.9° 66.0° 65.2°
2021 observed (anomaly) 66.6° (+1.0°) 64.7° (+0.8°) 65.3° (-0.7°) 65.9° (+0.7°)
2020 observed (anomaly) 69.0° (+3.4°) 66.7° (+2.8°) 69.6° (+3.6°) 67.2° (+2.0°)
2016 observed (anomaly) 66.6° (+1.0°) 66.0° (+2.2°) 67.1° (+1.1°) 67.4° (+2.2°)
2011 observed (anomaly) 65.7° (+0.1°) 63.6° (-0.3°) 65.4° (-0.6°) 64.3° (-0.9°)
2010 observed (anomaly) 66.1° (+0.5°) 65.2° (+1.3°) 66.8° (+0.8°) 65.6° (+0.4°)
2007 observed (anomaly) 67.1° (+1.5°) 65.8° (+1.9°) 67.4° (+1.4°) 67.1° (+1.9°)
Recent La Niña Averages (anomaly) 66.9° (+1.3°) 65.3° (+1.4°) 66.9° (+0.9°) 66.3° (+1.1°)

 

Assuming temperatures this fall were to average 1° F above normal, we could expend about 20 percent more energy than normal on air conditioning usage during the first half of the season, followed by a 25 percent energy savings for heating in November. 

Freezing temperatures usually reach the eastern Carolinas before Thanksgiving Day.  The average date of the first freeze ranges from October 29 in Lumberton, NC to November 21 in Georgetown, SC, but there is considerable year-to-year variability.  This first freeze spells an end to summer gardens as tomatoes, peppers, and many other vegetable and ornamental plants are killed.

In Wilmington, the season's first freeze has occurred as early as October 16 (in 1878) and as late as December 29 (in 1918).  But in Southport, NC freeze dates have been even more extreme: the 1945 growing season didn't end in Southport until temperatures finally fell to freezing on January 10, 1946!  That growing season of 327 days is the longest on record for any local city.

 

Average Date of the First Fall Freeze

Average dates of the first fall freeze for locations across southeast North Carolina and northeast South Carolina.  Click a station for detailed local info.

Location Average Date
Wilmington, NC November 17
Lumberton, NC October 29
Castle Hayne, NC November 5
Elizabethtown, NC November 2
Whiteville, NC November 2
Longwood, NC November 3
Southport, NC November 9
Florence, SC November 10
N. Myrtle Beach, SC November 16
Brookgreen Gardens November 15
Darlington, SC November 5
Dillon, SC November 2
Conway, SC November 17
Andrews, SC November 13
Lake City, SC November 10
Marion, SC November 1
McColl, SC November 1
Georgetown, SC November 21

 

 

 

Rainfall

Rain during the Fall months varies tremendously from year to year. Let's look at records over the past 10 years from Florence, SC. Rainfall amounts have ranged from less than 4" in 2013 and 2021...to over 20 inches in 2015 and 2016.  What could explain this huge difference?   It's not La Nina. Although La Nina does create a tendency for dry weather, the fall of 2016 had La Nina conditions, but also saw nearly two feet of rain in Florence.  The answer is rain amounts here in the fall depends largely on whether or not a hurricane strikes the area. Hurricane Matthew brought severe flooding to the Carolinas in 2016, as did Hurricane Florence in 2018. 2020 saw contributions from Tropical Storms Sally, Beta, Delta, and Eta, all of which produced rain.

Fall's seasonal rain total depends largely on whether or not a hurricane strikes the area. Hurricane Matthew brought severe flooding to the Carolinas in 2016, as did Hurricane Florence in 2018. Rainfall totals in 2020 had contributions from several tropical cyclones.  Years without a hurricane are often quite dry.

Fall in the Carolinas is associated with tremendous rainfall variability from year to year.  This is mainly due to the uneven distribution of Atlantic tropical storms and hurricanes. La Niña tends to create more active hurricane seasons compared to either neutral or El Niño years. 

Recent La Niña fall seasons with significant tropical cyclone rainfall here in the Carolinas include 2020 (Tropical Storms Sally and Beta) and 2016 (Hurricane Matthew).  Hurricane Matthew's flooding was, at the time, the worst on record for many parts of eastern South and North Carolina. 

In years without a landfalling tropical cyclone, it's tough for rainfall totals to reach the overall seasonal average regardless of whether we have La Niña, neutral, or El Niño conditions in place.  However La Niña typically shifts the jet stream and storm track northward and away from the Carolinas and can lead to consistently dry conditions.  Drought, aided by La Niña, either developed or was already ongoing across the eastern Carolinas during the 2021, 2011, and 2007 fall seasons.

Since individual tropical cyclones cannot be predicted at a seasonal scale, it's not possible to make a meaningful prediction for rainfall totals this fall.  The Climate Prediction Center's outlook of "equal chances" for below, near, or above normal rainfall is the best that science allows.

The following table shows how September through November rainfall compared to normal during each of the La Niña fall seasons over the past 20 years at four local cities.

  Wilmington Lumberton N. Myrtle Beach Florence
1991-2020 AVG. FALL RAINFALL 16.91" 10.17" 14.14" 10.58"
2021 observed (anomaly) 12.64" (-4.27") 3.68" (-6.49") 4.68" (-9.46") 3.66" (-6.92")
2020 observed (anomaly) 21.25" (+4.34") 18.38" (+8.21") 15.22" (+1.08") 12.81" (+2.23")
2016 observed (anomaly) 24.74" (+7.83") 20.84" (+10.67") 27.93" (+13.79") 23.51" (+12.93")
2011 observed (anomaly) 12.36" (-4.55") 8.92" (-1.25") 8.78" (-5.36") 5.74" (-4.84")
2010 observed (anomaly) 25.16" (+8.25") 10.49" (+0.32") 11.58" (-2.56") 11.05" (+0.47")
2007 observed (anomaly) 7.37" (-9.54") 3.00" (-7.17") 6.49" (-7.65") 5.43" (-5.15")
Recent La Niña Averages (anomaly) 17.25" (+0.34") 10.89" (+0.72") 12.45" (-1.69") 10.37" (-0.21")

 

 

Tropical Cyclones and Beach Hazards

This hurricane season has (so far) been unusually quiet with only five named storms through September 5.  For the first time since 1997 (and for only the third time since 1950) no tropical cyclones formed during the month of August in the Atlantic Ocean.  The Accumulated Cyclone Energy index (ACE) remains well below normal values as of early September.

The Climate Prediction Center continues to believe this season may yet see above-normal activity featuring 14 to 20 named storms, 6 to 10 hurricanes, and 3 to 5 major hurricanes which produce wind speeds of 115 mph or greater. 

August 2022 updated Atlantic Hurricane Season Outlook

 

Fall is typically the most active portion of the our Atlantic season.  Since 1870 when wind records began in Wilmington, 58 percent of all tropical cyclones which produced tropical storm force (39 mph) or greater gusts in the Port City have occurred in September or October.

Month Number of storms which produced 39+ mph gusts at the Wilmington Weather Bureau/NWS since 1870 Percent of all events
May 2 storms 3%
June 2 storms 3%
July 8 storms 11%
August 18 storms 25%
September 29 storms 40%
October 13 storms 18%

 

Tropical storms and hurricanes can have impacts on the beaches of North and South Carolina even when the storms are located thousands of miles away.  Long-period swells generated by hurricanes travel great distances across the ocean and can create large surf and dangerous rip currents when they reach the beaches.  Since 2004 when the National Weather Service in Wilmington began collecting daily surf reports from lifeguards, September has been the most active month for "moderate" or "strong" rip current reports -- often the result of waves generated by distant hurricanes.

     NOAA/USLA Rip Current Safety Toolkit

 

Relative incidence of weak, moderate, and strong reported rip currents at Wrightsville Beach, NC from 2004 through 2021

Monthly compilation of lifeguard supplied rip current reports from Wrightsville Beach 2004 through 2021. September has the highest incidence of moderate or strong rip currents of any month during the warm season.  Graphic: NWS Meteorologist Vicky Oliva.

 

Preparedness for hurricanes starts now.  Even when no storms are threatening the Carolinas, it's a good time to review your family's hurricane readiness plan.  NOAA maintains a list of resources for help get you ready here: https://www.noaa.gov/hurricane-prep

 

 

Coastal Flooding Potential

There are several periods this fall when astronomical tides will be large enough to cause concern for coastal flooding at our local beaches and along tidal creeks and rivers.  "Sunny day" flood events occur when strong winds or storms are not necessary to create minor coastal flooding due to tides high enough by themselves.  Specific dates when this type of flooding could occur include:

  • September 8-13
  • September 28-30
  • October 8-12
  • October 25-29
  • November 7-9
  • November 22-27

 

Tides will be particularly high during September's Full Moon (September 8-13) and during November's New Moon (November 22-27.)  These are "perigean spring tides" when the Moon is at its closest approach to Earth and the Moon's tidal influence is strongest.

 

September 2022 tides

September astronomical tides

October 2022 astronomical tides

October astronomical tides

November 2022 astronomical tides

November astronomical tides

 

Landfalling tropical storms or hurricanes can produce coastal flooding regardless of the astronomical tides.  And as we move toward the end of fall, non-tropical storms called Nor'easters can produce strong winds and coastal flooding too.

 

 

River Flooding Potential

Drought conditions that covered most of the eastern portions of North and South Carolina this spring ended due to near-normal rainfall during the summer months.  However most rivers across the eastern Carolinas have remained below normal levels.  Conditional river simulations from the NWS Southeast River Forecast Center (SERFC) show the chances for river flooding this fall are below normal, likely a consequence of low river flow as fall begins.

Along the Waccamaw River at Conway, SC, a normal fall season sees about a 30 percent chance of the river reaching flood stage (11 feet) at least once.  The SERFC conditional simulation for this year (2022) shows only a 20 percent chance of the river reaching flood stage. 

Waccmaw River at Conway conditional stage forecast through the Fall

 

Conditional river simulations and other current and forecast river information are available for a number of points along local rivers:

 

River flooding unleashed by Hurricane Florence in September 2018 destroyed a section of U.S. Highway 421 north of Wilmington

River flooding unleashed by Hurricane Florence in September 2018 destroyed a section of U.S. Highway 421 north of Wilmington

Waccamaw River

Lumber River

Cape Fear & Northeast Cape Fear Rivers

Black Creek & Pee Dee River

Lynches River

Black River

 

 

Additional Reading

NOAA Hurricane Season Outlook August 2022 Update:  https://www.cpc.ncep.noaa.gov/products/outlooks/hurricane.shtml

CPC: ENSO Recent Evolution, Current Status and Predictions

National Ocean Service High Tide Bulletin for Fall 2022:  https://oceanservice.noaa.gov/news/high-tide-bulletin/fall-2022

NWS Wilmington Tropics Main Page:  https://www.weather.gov/ilm/tropical

NWS Wilmington Significant Local Events Archive:  https://www.weather.gov/ilm/SignificantLocalEvents

Daily Climate Normals and Records for Wilmington, Florence, North Myrtle Beach, and Lumberton

 

Research and Author: Tim Armstrong
Last Updated: September 8, 2022