Tropical Storm Debbie will continue to bring heavy rains to the southeastern United States on Wednesday and Thursday, with the slow-moving storm moving slowly along the South Carolina coast. Although the center of Debbie moved over the water Tuesday night, the storm did not intensify much and rainfall has decreased significantly since Tuesday. The large number of storms now accumulating is more the result of Debbie's lackadaisical actions than the result of extremely heavy rainfall rates. As a result, some of the most severe local flash flooding risks are decreasing, while larger river flooding problems are increasing.
At 11 a.m. ET Wednesday, Debbie was located about 55 miles southeast of Charleston, South Carolina, with winds intensifying to 60 mph, moving slowly northeast at 5 mph. As dry air penetrated the inland side of Debbie, showers and thunderstorms (convection) were concentrated almost entirely on the eastern half of the storm, giving the storm an asymmetrical and somewhat cluttered appearance on radar – although visible during the day There are a lot of clouds in the circulation, as shown in the satellite loop below and the image at top.
Debbie Weather Forecast
The center of Debbie is expected to remain off the coast of South Carolina by Thursday morning, with sea temperatures of 28-29 degrees Celsius (82-84°F). However, this large and poorly organized storm is not structured for rapid intensification, and the National Hurricane Center predicts that Debbie's top sustained winds will increase by just 5 mph to 65 by the time of its second landfall Thursday morning. miles per hour. During this time, Debbie will be crawling at a forward speed of nearly 5 mph. This will allow the storm to bring additional heavy rainfall to much of coastal South Carolina and southern North Carolina, which is typically just northeast of areas that receive the heaviest rainfall early Wednesday.
Debbie's historic flooding across the southeastern United States will finally begin to weaken on Friday and Saturday, when a trough of low pressure pulls the storm toward the northeast. However, Debbie's flooding threat will then spread into the mid-Atlantic and northeastern United States, where widespread rainfall of 4-8 inches is expected (Figure 1). The National Oceanic and Atmospheric Administration's (NOAA) excess rainfall discussion, held at 8:36 a.m. ET on Wednesday, lists large areas of Pennsylvania, New York and Vermont as being at “moderate risk for excessive rainfall and flash flooding on Friday.” ” (see tweet below).
Debbie-induced Pre-Rain Event (PRE) hits New York/New Jersey
After a hurricane makes landfall, heavy rainfall may develop poleward and more than 500 miles downstream, a phenomenon known as a precursor rainfall event (PRE). It was this premonitory weather that flooded parts of the mid-Atlantic and Northeast with torrential rains on Tuesday, and Debbie is expected to sweep through the region for days. Fortunately, Debbie's south-to-north movement across the interior Northeast on Friday will spread out vertically and sit just inland of the east-west corridor of Tuesday's heavy rain, limiting the area of the trail where the two intersect.
Severe flash flooding was reported in New York City on Tuesday night, particularly in the Bronx, with some highways closed and six people involved in rescue operations on the Cross-Island Parkway. The heaviest rainfall was recorded in Bergen County, New Jersey, and Bronx County, New York, where more than five inches fell in less than eight hours. As of late Tuesday night, some of the larger totals include:
Bogota, New Jersey: 5.47 inches
New York (Fordham, Bronx), New York: 5.38 inches
New York (Bronx City Island), New York: 4.76 inches
Port Washington, NY (Nassau County): 4.62″
Dix Hills, NY (Suffolk County): 3.91″
Caldwell, New Jersey: 3.96 inches
The highest single-day rainfall totals in the region measured by the CoCoRaHS Volunteer Rainfall Network on Wednesday morning include:
Pennington, New Jersey: 7.76 inches
Indiana, Pennsylvania: 4.50 inches
Hebron, Maryland: 3.95 inches
Amityville, New York: 3.37 inches
Stamford, Connecticut: 3.14 inches
Major rivers flood in Florida, Georgia and South Carolina
Three rivers in Florida, two rivers in Georgia and one river in South Carolina experienced severe flooding Wednesday morning. Severe flooding is expected later this week on five rivers in North Carolina, two rivers in South Carolina, and one river in Florida.
More than 17 inches of rain fell in South Carolina
Rainfall north of Debbie Center was generally less on Wednesday morning than Tuesday morning, as measured by CoCoRaHS' daily report. Widespread flooding of 4 to 8 inches was reported in central and southeastern South Carolina and adjacent areas along the coasts of Georgia and North Carolina. The highest state totals in the 24 hours ending Wednesday morning include:
- Murrells Inlet, South Carolina: 8.00″
- Calabash, North Carolina: 5.82 inches
- Lovettsville, Virginia: 2.38 inches
As of 10 a.m. ET on Wednesday, August 7 (Sunday through Wednesday morning), the highest four-day storm totals in each state from Debbie are from the CoCoRaHS network. Compared with the historical record of tropical cyclones, they include the following:
- Florida: 19.67”Lake City ESE 2.8 miles (Easy 1950 state record 45.20 inches)
- South Carolina: 17.27 inches5.3 miles southeast of Somerville (2018 Florence record 23.63 inches)
- Georgia: 13.44 inches5.3 miles northeast of Rincon (National record 27.85 inches from Alberto 1994)
- North Carolina: 7.22 inches1.9 miles northeast of Calabash (2018 Florence State Record 35.93 inches)
At 8:36 a.m. ET Wednesday, the National Oceanic and Atmospheric Administration's (NOAA) excess rainfall discussion placed the South Carolina/North Carolina coastal border region at “high risk” for heavy rainfall of 4 to 8 inches Wednesday, It warned that “there is a possibility of heavy rainfall in the area for 48 hours.”
The high risk area for Thursday is expected to cover similar areas but expand into central North Carolina, where 3-6 inches of rain are expected. In the United States, only about 4% of days are classified as high-risk areas, but these areas account for about one-third of all flood deaths and about 80% of flood-related losses.
Lower likelihood of Caribbean tropical wave development
The likelihood of tropical cyclones forming from tropical waves moving through the central Caribbean Sea is decreasing. The wave is moving in moist conditions and over seas that are about 1 degree Celsius (1.8 degrees Fahrenheit) warmer than average, but persistent northwest wind shear is cluttering its shower and thunderstorm field. In the Tropical Weather Outlook released at 8 a.m. ET on Wednesday, the National Hurricane Center gave the system an almost zero chance of becoming at least a tropical depression by Thursday and only a 10 percent chance by next Wednesday. No other systems are expected in the Atlantic Ocean for at least the next week.
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