Chesapeake Bay Climate Impacts Summary and Outlook

Chesapeake Bay Watershed Climate Impacts Summary and Outlook: Fall 2019



  • Fall 2019 saw above-average temperatures compared to normal for the majority of the Chesapeake Bay watershed in September and October and below-average temperatures for November.
  • October and September 2019 were among the ten hottest Octobers and Septembers on record for several locations, including Washington, D.C. and Harrisburg, Pennsylvania.
  • Washington Dulles Airport experienced its third hottest September on record and its eighth coldest November on record.


  • This fall, the Chesapeake Bay watershed experienced less precipitation than historical averages.
  • September 2019 ranked among the top ten all-time driest months on record for Baltimore, Maryland and Washington, D.C.
  • Hot, dry weather during the fall months led to moderate and severe drought in Virginia, Maryland, Delaware, a small portion of West Virginia's Eastern Panhandle, and south-central Pennsylvania.

Tropical Storms and Hurricanes

  • An analysis of historic tropical storms and hurricanes shows that the majority impact this region in September, then August and that the distribution of storms across hurricane season months has remained relatively constant over time.
  • Under future climate change, the Mid-Atlantic region could expect more tropical storms and hurricanes of higher intensity, but research on the total number of storms is mixed.

Part 1: Significant Weather Events

Hurricane Dorian

Even though the center of Hurricane Dorian never made landfall in the region, the storm's outer bands impacted the eastern parts of Maryland and Virginia from September 5–7.1 Hurricane-force wind gusts of up to 83 mph were recorded at the Chesapeake Light Tower, which is approximately 1000 feet off the beach and 13 miles from the coast of Virginia Beach.2 Tropical storm force wind gusts of up to 70 mph downed trees, knocked down power poles, and caused roof damage, particularly in the Hampton Roads region of Virginia.3 Tidal flooding occurred along the Chesapeake Bay and its tributaries, with major flood stages of 6 ft and 5.5 ft surpassed at the Chesapeake Bay Bridge Tunnel and Kiptopeke, Virginia, respectively.4 The flooding led to closed roads and stranded vehicles.5 Hurricane Dorian contributed to additional moderate to heavy rainfall in the Hampton Roads region and on Maryland's Eastern Shore, with the greatest storm totals approaching 4 inches.6 As a result, multiple school districts and universities cancelled classes, and government offices were closed.7

Heavy Rainfall

In the month of October, several storms brought much-needed rain to the region, resulting in the ninth wettest October for Washington, D.C. on record.8 This precipitation eased drought conditions across much of the watershed, supporting crop growth and pastures, allowing burn bans to be lifted, and improving water levels on area waterways.9,10

A strong storm stalled off the East Coast from October 8 through 12, resulting in persistent northerly winds that created elevated water levels, which in combination with high waves, caused tidal flooding in the Chesapeake Bay and along its tributaries.11 Most locations experienced minor or moderate flooding, but several sites along Virginia’s Northern Neck and Maryland’s Eastern Shore experienced major flooding.12 Preliminary data showed the tide height measured at Chesapeake Bay at Cambridge, Maryland reached 4.68 feet on October 12, which ranks as the fourth highest water level since 1980 (3.5 feet is considered flood stage, and 4.5 feet is considered a major flood stage).13

Coastal flooding during high tide in Cambridge, Maryland.

Photo by Dorchester County Emergency Management

A few days later, from October 16 to 17, a rapidly strengthening coastal storm brought up to 2 inches of rain and wind gusts of up to 57 mph to the watershed, causing areas along the Chesapeake Bay once again to experience tidal flooding.14,15

The remnants of tropical storm Nestor moved through southeastern Virginia from October 20-21, bringing gusty winds and moderate to heavy rain to southern parts of the watershed, with southeastern Virginia and eastern Maryland receiving up to 5 inches of rain.16

Severe Weather

A line of severe thunderstorms blasted through the region on October 31. Storm reports indicated that two tornadoes, an EF-0 and an EF-1, caused damage in Chesapeake, Virginia, and strong winds knocked down trees and wires in many locations within the watershed.17 The storms contributed to numerous power outages, as well as two deaths.18 Heavy rain accompanied the storms and caused flooding in several locations. For example, flooding led to the closure of Interstate 83 in central Pennsylvania, and several cars were stranded in floodwaters in Baltimore.19,20

A low pressure system made its way up the East Coast from November 16 to 18. Fog and freezing drizzle in Virginia’s Shenandoah Valley, particularly at higher elevations, created icy roads that contributed to a bus crash on Interstate 64 that sent at least 20 people to the hospital.21, The storm combined with high tide that occurred simultaneously resulted in coastal flooding.22,23,24,25

On November 27 and 28, wind gusts of up to 68 mph downed trees and powerlines in the southern parts of the Chesapeake Bay watershed causing minor disruptions to Thanksgiving travel due to power outages, closed roads, and flight delays. 26,27,28

Damage caused by a tornado in the City of Chespeake, Virginia, on October 31.

Photo by National Weather Service

Extreme Temperature

Daytime and nighttime temperatures were persistently warm during the month of September, making it one of the ten hottest Septembers on record for some locations within the Chesapeake Bay watershed. Richmond, Virginia; Washington, D.C.; and Dulles Airport, Virginia had their third hottest Septembers, while Baltimore, Maryland had its fifth hottest, and Harrisburg, Pennsylvania and Charlottesville, Virginia had their seventh hottest Septembers.29

The heat continued into October, and between October 1 and 3, maximum temperatures reached 27 degrees F warmer than normal. Minimum temperatures were as much as 23 degrees F warmer than normal.30 October 2 was the hottest October day on record for Baltimore, Maryland, the Washington Dulles International Airport, and Washington, D.C. as high temperatures soared into the mid- to upper-90s.31 Other sites in the watershed, including Norfolk, Virginia; Binghamton, New York; and Harrisburg, Virginia also experienced temperatures that ranked among the top five hottest on record for October.32 Overall, Richmond, VA, had its tenth hottest fall on record since 1897 with an average temperature of 62 degrees F, which was 1.8 degrees F warmer than normal. 33

By contrast to a warm September and October, November was saw periods of extreme cold across the region. Binghamton, New York had its fifth coldest November on record since 1951 with an average temperature of 32.8 degrees F, which was 5.5 degrees F colder than normal. 34 Dulles Airport had its eighth coldest November on record since 1962, with an average temperature of 42.2 degrees F, which was 4.2 degrees F colder than normal.35


Along with above-normal temperatures in September, the region also received below-normal precipitation. Overall, September 2019 ranked the second driest September on record for Baltimore, Maryland, with 0.16 inches in total monthly precipitation, and for Washington Dulles International Airport, with 0.41 inches in total monthly precipitation.36 September 2019 was also the fourth driest for Washington, D.C., with 0.25 inches in total monthly precipitation, and Richmond, Virginia, with 0.42 inches in total monthly precipitation.37 When compared to all months of the year, September 2019 ranked among the top ten all-time driest months on record for Baltimore and Washington, D.C.38

This hot, dry weather led to moderate and severe drought in Virginia, Maryland, Delaware, a small portion of West Virginia's Eastern Panhandle, and south-central Pennsylvania.39 The last moderate to severe drought conditions in the region occurred in Maryland and Virginia in January-February 2018.40 Part 3 of this climate summary describes anticipated drought conditions for Winter 2019-2020.


Drought conditions had a severe effect on agriculture. In late September, the topsoil was considered dry or very dry in all of Delaware, 99% of Maryland, and 88% of Virginia, and pasture conditions were rated poor or very poor for 74% of Virginia.41,42 Planting of fall crops was also delayed in Caroline and King George counties in Virginia and Sussex County in Delaware, and some crops were slow to emerge in Frederick, Howard and Montgomery Counties in Maryland. 43,44 Dry conditions contributed to lower soybean yields in parts of Delaware and Maryland but allowed for a quick corn harvest in Maryland.45,46 Botetourt County, Virginia was one of several counties in Virginia to declare a disaster because of the drought, potentially making farmers eligible for government assistance.47

Fire Risk

Drought increased the risk of wildfires in the region. Burn bans were enacted in all 55 West Virginia counties, at least 24 Virginia counties, and along Maryland’s Eastern Shore, with Wicomico County issuing its first burn ban since 2012.48 A brush fire at Jefferson National Forest in Virginia shut down a ten-mile section of the Appalachian Trail and another fire in Bedford County, Virginia took almost a week to for firefighters to extinguish.49,50 Two fields in Baltimore County, Maryland caught fire.51

Fall Foliage

The dry conditions affected fall foliage in some areas, with muted colors and drought-stressed leaves falling earlier by a month or more in western Virginia.52 Peak fall foliage generally occurs in mid-October in this region.

Algae Bloom

During the drought, water levels on rivers, streams, and other waterways fell to below-normal levels.53 Little rainfall and warm temperatures contributed to a large algae bloom on the James River in Virginia in September and early October, which is unusual, as blooms normally peak during the summer months.54

Part 2: Seasonal Temperature and Precipitation


Figure 1 shows an analysis of Fall 2019 (September – November 2019) average temperature compared to the climate normal, defined as the average temperature from 1981 to 2010. This analysis indicates above-average temperatures from normal for the southern two-thirds of the Chesapeake Bay watershed. Portions of central and northern Pennsylvania and southern New York experienced below average temperatures. Areas within the southern half of the watershed, particularly in in Virginia and Maryland, experienced temperatures that were 2–4 degrees above normal.

Figure 1. September 1, 2019 – November 30, 2019 Departure from Normal Temperature (°F)

Note: Normal temperature is based on fall seasonal average temperature data from 1981-2010. Red indicates above-average temperature.

Source: Northeast Regional Climate Center, 2019.

Figure 2 shows the fall season’s variability in daily average temperature departures from normal at the Washington Dulles Airport in Virginia. While the average seasonal temperature for the region was near normal, the daily temperatures showed large departures for normal. In the case of Dulles Airport, this location saw record highs and lows throughout the season.

Figure 2. Daily Average Temperature Departure from Normal September-November 2019 for Dulles, VA


From September 1 through November 30, 2019, precipitation departures from normal, seen in Figure 3, show that the majority of the Chesapeake Bay watershed experienced less precipitation than historical averages, with several areas experiencing only 50–75% of their normal precipitation for the period. As recently as October 15, the U.S. Drought Monitor indicated areas of severe and moderate drought in Maryland, Delaware, and Virginia. 55 These areas of drought have since improved, due to recent rainfall events, and as of November 27, only central southern Virginia was experiencing moderate drought, with the rest of the region experiencing, at worst, abnormally dry conditions.56

For more data on historical trends and future projections of seasonal precipitation, see Part 4 of the Winter 2018-2019 Climate Summary. More information on how recent precipitation and temperature compares to historical trends for the East Coast, including the Mid-Atlantic region, can be found using the Southeast Regional Climate Center’s Climate Perspectives tool.57

Figure 3. September 1, 2019 – November 30, 2019 Percent of Normal Precipitation

Note: Normal seasonal precipitation is based on precipitation data from 1981-2010. Oranges and reds indicate below-average seasonal precipitation.

Source: Northeast Regional Climate Center, 2019.

Part 3: Winter 2019 Outlook

Temperature and Precipitation

As of November 21, 2019, NOAA's Climate Prediction Center forecasted a 33–40% chance of above normal precipitation for December 2019 – February 2020 in the Mid-Atlantic region.58 They showed a 33-40% chance of temperatures above normal for the Chesapeake Bay Watershed.

Drought Incidence

The U.S. Seasonal Drought Outlook predicts how drought may change across the United States, categorizing areas by whether drought could develop or become more or less intense. As of November 21, 2019, the outlook indicated removal of drought conditions for Southern Virginia.59 The Chesapeake Bay region has experienced severe to extreme droughts in the past, most notably in the mid-1980s, the late 1990s and the 2000s.60

Climate Circulation Patterns

NOAA's Climate Prediction Center, which monitors the likelihood of occurrence of El Niño and La Niña climate phenomena, had no alerts or warnings active as of December 3, 2019, and predicted neutral conditions in the Pacific Ocean, rather than either El Niño or La Niña.61 In the absence of these two phenomena, other climate patterns such as the Arctic Oscillation (AO) can play an important role in winter weather.62 The AO, which characterizes atmospheric circulation patterns over northern portions of the Northern Hemisphere, has two phases—negative and positive. When the AO is negative, the Northeastern United States is more likely to experience Nor’easters and outbreaks of polar air.63

Part 4: Hurricanes and Tropical Storms in a Changing Climate

Recent increases in hurricane intensity are partially linked to rising sea surface temperatures in the regions where North Atlantic hurricanes form.64 For over a decade, research has shown that hurricane activity, including changes in their frequency, along the U.S. Atlantic coast is sensitive to warm sea surface temperatures, by shifting storm tracks and changing the formation of hurricanes and tropical storms.65,66,67

This section details the historical trends in the frequency, magnitude and impact of hurricanes and tropical storms, as well as provides an overview of how scientists expect these storms to change under future climate.

Historical Trends in Hurricanes and Tropical Storms

Key Findings

  • Since the 1980s, North Atlantic hurricanes have increased in intensity, frequency, and duration. The strongest hurricanes, categories 4 and 5, have also increased in frequency.68 The North Atlantic includes the Atlantic Ocean north of the equator, the Gulf of Mexico, and the Caribbean Sea.69
  • The Mid-Atlantic and Northeast regions have historically experienced a lower frequency of tropical storms and hurricanes compared to other regions of the United States, receiving 6% of such storms annually over the continental U.S. from 1990 to 2017.70
  • Figure 4 below shows the number of storms by month (top panel) affecting the Mid-Atlantic region from the National Oceanic and Atmospheric Administration (NOAA) National Hurricane Center's North Atlantic hurricane database (or HURDAT) for hurricanes and tropical storms.71
  • From the top panel of Figure 4, the majority of storms fall in this region in September, then August. The distribution of storms across hurricane season months has remained relatively constant.
  • According to the data available for the Mid-Atlantic, as shown in the bottom panel of Figure 4, no significant changes in the intensity of frequency of hurricanes or tropical storms is apparent.

How to Use the Tool

To view changes in hurricane frequency by month (top panel) and by windspeed (bottom panel), users can select a time period of interest (top right slider), as well as a specific hurricane category or tropical storm. Users can view a pop-up window of hurricane or tropical storm name, windspeed, and other useful information by hovering their mouse over a given data point on the two figures.

Technical Notes

Major hurricanes are those at a Saffir-Simpson Hurricane Wind Scale of 3 or 4 (no Category 5 storms appear in the HURDAT database), and minor hurricanes are those at a Saffir-Simpson Hurricane Wind Scale of 1 or 2. The Hurricane Category filter allows users to select the magnitude of hurricane by Saffir-Simpson Hurricane Wind Scale. More information on the Saffir-Simpson Hurricane Scale can be found at: Mid-Atlantic is defined as the states of New York, New Jersey, Pennsylvania, Delaware, Maryland, Washington, D.C., Virginia, West Virginia. Hurricanes and Tropical Storms that made landfall in any bordering states, such as North Carolina, were also included as these storms may have impacted areas outside of where they made landfall. While the data used for this figure is generally based on observed records, estimates of the magnitude, windspeeds and landfall patterns of hurricanes and Tropical Storms included in the HURDAT database are subject to limitations of this dataset. More information on HURDAT can be found at:

Key Findings

  • Figure 5, below, shows the reported crop damage and reported property damage in United States dollars ($) for all hurricanes and tropical storms in the NOAA National Centers for Environmental Information (NCEI) Storm Events database occurring between 1996 to 2018.72
  • From reported damage in the NCEI database, the most impacted counties are those in Maryland, New Jersey and eastern Virginia.

How to Use the Tool

To view changes in reported damage from hurricanes and tropical storms, users can select a time period of interest (top right slider), a state of interest (drop down menu), as well as the type of reported damage. Users can also view a pop-up window with additional hurricane impacts by hovering their mouse over a given county.

Technical Notes

Dollar values shown are reported in the year in which a storm event occurred. Hurricane and tropical storm events are reported by National Weather Service (NWS) forecast zone. In some cases, the forecast zone may include multiple counties, or a single county may include multiple forecast zones. Where forecast zones include multiple counties, reported impacts (injuries, deaths and damage) have been split equality between the included counties. Events occurring in counties with multiple forecast zones have not been merged. The NCEI database is a self-reported database consisting of damage data reported by states and agencies impacted by natural disasters. As such, it is limited by the accuracy, completeness and number of locations that reported natural disaster impacts.

Climate Change and Tropical Storms and Hurricanes

  • The Mid-Atlantic region could expect more category 4 and 5 storms, but research on the number of storms overall is mixed.
    • Multiple studies suggest that the number of the most intense Atlantic hurricanes is projected to increase.73, 74
    • Scientists project a 5 to 7% increase in the intensity of tropical cyclones (hurricanes and tropical storms) during the next century when compared to present-day simulations.75
    • Researchers project that category 4 and 5 hurricanes could double in frequency by the end of the 21st century.76
    • The highest increase in the frequency of category 4 and 5 storms could occur in the Western Atlantic, between 20°N and 40°N. This area encompasses much of the Mid-Atlantic region, as the 40th parallel north runs near the southern state line of Pennsylvania.77
    • One study showed that annual increases in the number of category 4 and 5 storms could be on the order of 24% and tropical cyclones with winds over 145 mph could increase by 59%. 78
  • Research on future changes in the number of tropical cyclones is mixed.
    • One study found that due to shifting storm tracks and reductions in tropical cyclones over the southern Gulf of Mexico, and the Caribbean, the number of storms could increase in the Mid-Atlantic by approximately 1 to 1.5 per decade.79
    • One study found an increase in the number of named tropical cyclones in the Northern Atlantic region of approximately 35% compared to 1982–2009.80
    • Multiple studies also suggest that the overall number of tropical cyclones is projected to decrease.81,82
  • Floods that result from tropical cyclone activity could increase in frequency in coastal areas of the Mid-Atlantic.
    • Researchers found that the historical 100-year flood event could occur annually in coastal regions in the Mid-Atlantic, due to both rising sea levels and changes in tropical cyclone activity.83

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The MARISA Seasonal Climate Impacts Summary and Outlook is a quarterly series produced by the Mid-Atlantic Regional Integrated Sciences and Assessments (MARISA) program, a collaboration funded by NOAA through RAND and researchers at Pennsylvania State University, Johns Hopkins University, Cornell University, and the Virginia Institute of Marine Science. This series draws information from regional climate centers, news and weather information, and regional-specific climate datasets for the benefit of policymakers, practitioners, residents, and community leaders in the Chesapeake Bay Watershed. Projections of weather and climate variability and change in the Chesapeake Bay Watershed come from the best available scientific information. For any questions or comments, please contact Krista Romita Grocholski at

This edition of the MARISA Seasonal Climate Impacts Summary and Outlook was authored by Michelle E. Miro (RAND Corporation), Krista Romita Grocholski (RAND Corporation), Samantha Borisoff (Cornell University), Jordan R. Fischbach (RAND Corporation), Arthur T. DeGaetano (Cornell University), Pamela H. Braff (Virginia Institute of Marine Science), and Stephanie Tanverakul (RAND Corporation).

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