Hurricane 2021 Forecast

 

Ocean City, Maryland (Photo Credit: Ashley Adams)

The National Oceanic and Atmospheric Administration (NOAA) recently issued its forecast for the 2021 Atlantic hurricane season.  NOAA expects an above average season with 13 to 20 named storms, including 6 to 10 hurricanes of which 3 to 5 will become major hurricanes.  NOAA has a 70% confidence level in these totals.  “Ana,” the first named storm, has already developed.  So, for a seventh consecutive year, the hurricane season got underway prior to its official start on June 1.

In 2016 and 2020, there also were two named Atlantic storms before the season officially got under way.  It’s important to note that earlier this spring NOAA updated its average seasonal totals to reflect the 30-year period of 1991-2020, rather than 1981-2010.  An “average” Atlantic hurricane season now has 14 tropical storms, 7 hurricanes and 3 major hurricanes compared to 12, 6 and 3 previously.  That’s not a surprise since seven of the last 10 Atlantic hurricane seasons have been busier than average.

NOAA’s forecast is similar to the forecast the team of Colorado State University scientists released in April that called for 17 named tropical storms, 8 hurricanes and 4 major hurricanes.  A “major” hurricane is defined as a Category 3 or higher on the Saffir-Simpson Hurricane Wind-Scale with sustained winds of 111 mph or higher.   

A major factor that NOAA used in issuing its forecast is the status of ENSO (El Nino Southern Oscillation).  That essentially means whether or not there is an episode of El Nino or La Nina present.  When El Nino is present, conditions tend to be less favorable for tropical development in the Atlantic due to cooler than average sea surface temperatures and above average levels of wind shear (winds that change direction with altitude).  La Nina or ENSO-neutral (neither El Nino or La Nina) conditions contribute to a more favorable environment for tropical development in the Atlantic Ocean. 

ENSO is currently in a neutral phase with the potential return to La Nina conditions later this summer or early fall.  That would enhance conditions for tropical development in the Atlantic Ocean Basin, which also includes the Gulf of Mexico and Caribbean Sea.  While ENSO-status is a prominent factor into whether or not the Atlantic has an active hurricane season, there are other contributing factors such as whether or not sea surface temperatures are warmer than average and how much dust is blowing west from the Sahara Desert into the tropical Atlantic.  Wind shear and dry desert air both interrupt the circulation of tropical systems.

It’s less important how active a hurricane season than where any potential storms track.  An active season could see few, if any, landfalling tropical systems while a below average season could see destructive and/or deadly hurricanes.  Such was the case in both 1983 and 1992, which each featured only one major Atlantic hurricane.  However, those hurricanes were Alicia and Andrew that were damaging and deadly.

Weather Quiz

 

True or False.

Since the National Hurricane Center named “Ana” a subtropical storm, it officially became the third time in the last 20 years that “Ana” became a named storm prior to June 1.

Major Shift in DC’s Weather Pattern

 

The weather in the Nation’s Capital during the first half of May 2021 has been both cooler and drier than average.  May is normally one of the nicest weather months of the year in D.C. with average highs in the 70s.

During the first half of May, Washingtonians have experienced predominantly cooler than average weather, including every day since May 6.  That’s resulted in an average monthly temperature (combining daily high and low temperatures) for May 1 – May 17 of 2.7° below average.  Many D.C. Area residents may recall that last May finished more than 2° cooler than average also.

However, there will be a major shift in the weather pattern this week to more summer-like weather as the jet stream changes course.  High temperatures today will flirt with 80° before soaring into the 80s tomorrow.  Highs will reach the low 90s later in the week in parts of the D.C. Metro Area.  That would be right on schedule as the average first 90° day of the year in Washington, D.C. occurs on or around May 18. 

While there wasn’t any 90° heat in the Nation’s Capital last May for only the second time in a decade, Washingtonians have averaged between one and two 90° days in May dating back to the early 1990s.  Not surprisingly given the shift in the weather pattern, NOAA’s Climate Prediction Center expects the next two weeks to be warmer than average in the Mid-Atlantic Region.  That means there’s a good chance DC’s average monthly temperature for May 2021 will finish very close to average despite the cool start to the month.

This month has also had a gotten off to a drier than average start with only 0.69” of rain as of May 17.  The Nation’s Capital is running a rainfall deficit of more than 2” since March 1.  Some may find that hard to believe since there have been a fair number of days with rain.  None of the rain has been particularly heavy, though.  My colleagues and I on the WUSA9 Weather Team don’t expect rain before the weekend at the earliest.

The good news about the warm temperatures arriving by the end of the week is that it won’t be particularly humid.  The warmer temperatures will actually feel pleasant absent the higher relative humidity levels so common across the D.C. Metro Area in July and August.