Satellite image
Visible satellite image of 98L at 10:20 a.m. EDT Thursday, July 9, 2020. (Image credit: NOAA/RAMMB)

An area of low pressure located over the coastal waters of southeast North Carolina on the morning of Thursday, July 9 is likely to develop into a tropical depression or subtropical depression or storm by Friday, July 10.

The system, designated 98L by NOAA’s National Hurricane Center, was moving northeast to north-northeast at 5-10 mph on Thursday morning. This motion will keep the center of the system close to the coast of North Carolina through Friday morning. Satellite loops show that 98L has a high amount of spin, and the disturbance is generating a large amount of heavy thunderstorm activity over the coastal waters of North Carolina and the Outer Banks.

Radar view
Figure 1. Radar image of 98L at 10:44 a.m. EDT Thursday, July 9, 2020. (Image credit: National Weather Service Morehead City, NC, via Mark Nissenbaum)

These thunderstorms were growing more organized on Thursday morning, but the heaviest activity was displaced more than 100 miles from the center of circulation. This is characteristic of a subtropical storm rather than a tropical storm, making it likely that 98L may be initially classified as subtropical rather than tropical. The difference between the two types of storms is not important for a weak system like 98L, whose main threat will be heavy rain regardless of whether it is classified as tropical or subtropical. An Air Force hurricane hunter aircraft is scheduled to investigate 98L on Thursday afternoon.

Conditions are favorable for development, as the warm Gulf Stream current lies just off North Carolina coast, where ocean temperatures are about 28 degrees Celsius (82°F). Wind shear is a moderate 10-15 knots, and mid-levels of the atmosphere are moist, with a relative humidity near 70%.

Figure 2
Figure 2. Track forecast for 98L beginning at 2 a.m. EDT Thursday, July 9, 2020, from the operational GFS model (heavy black line) and its 21 ensemble members (thin lines color-coded by 98L’s predicted central pressure). (Image credit: tropicaltidbits.com)

Forecast for 98L

The best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – show strong support for development of 98L by Friday. Steering currents will carry 98L to the north-northeast or northeast through Saturday, July 11, when the system likely will move inland over New England. With the waters cooling as 98L heads northeast and limited time over water, the system is unlikely to undergo significant intensification. The likely range for 98L’s peak maximum sustained winds will be 35-50 mph, over the waters offshore to the east of the system’s center.

Figure 3
Figure 3. Precipitation forecast for the five-day period ending at 8 a.m. EDT Tuesday, July 14, 2020. (Image credit: NOAA)

Regardless of development, heavy rains will be the main threat from 98L, which is expected to bring widespread rains of one to three inches to much of the mid-Atlantic and northeast U.S. coast, with up to five inches in some locales (Figure 3). In its 8 a.m. EDT July 9 Tropical Weather Outlook, the National Hurricane Center gave 98L two-day and five-day odds of development of 80%.


7/8 Original Post: Low-pressure system off Carolinas likely to become tropical depression or tropical storm this week

Satellite image
Visible satellite image of 98L at 10:30 a.m. EDT Wednesday, July 8, 2020. (Image credit: NOAA/RAMMB)

An area of low pressure located over South Carolina on the morning of July 8 is likely to develop into a tropical depression or tropical storm off the coast of North Carolina by Friday, July 10.

The system, designated 98L by NOAA’s National Hurricane Center, was moving northeast at about 10 mph on Wednesday. This motion is expected to bring the center of 98L close to or just offshore the coast of North Carolina on Thursday. Satellite loops show that 98L has a high amount of spin, and the disturbance is already generating a large amount of heavy thunderstorm activity over the coastal waters of South Carolina and North Carolina. These thunderstorms were growing more organized on Wednesday morning, with one notable spiral band forming.

If the center of 98L does move offshore, conditions will be favorable for development, since the warm Gulf Stream current lies just offshore of the North Carolina coast, where ocean temperatures are near 28 degrees Celsius (82°F). Wind shear will be a moderate 10-15 knots, and mid-levels of the atmosphere will be moist, with a relative humidity near 70%.

Figure 1
Figure 1. Track forecast for 98L beginning at 2 a.m. EDT Wednesday, July 8, 2020, from the operational GFS model (heavy black line) and its 21 ensemble members (thin lines color-coded by 98L’s predicted central pressure). (Image credit: tropicaltidbits.com)

Forecast for 98L

The best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – show strong support for development of 98L into a tropical depression or tropical storm by Friday at the latest. Steering currents will carry 98L to the north-northeast or northeast through Saturday, July 11, when the system will likely move inland over Massachusetts. With the waters cooling as 98L heads northeast, and limited time over water, the system is unlikely to undergo significant intensification. The likely range for 98L’s peak maximum sustained winds will be 35-55 mph, over the waters offshore to the east of the system’s center.

Figure 2
Figure 2. Precipitation forecast for the five-day period ending at 8 a.m. EDT Monday, July 13, 2020. (Image credit: NOAA)

Regardless of development, heavy rains will be the main threat from 98L, which is expected to bring one to three inches to much of the mid-Atlantic and northeast U.S. coast, and up to five inches to the Outer Banks of North Carolina (Figure 2). In its 8 a.m. EDT July 8 Tropical Weather Outlook, the National Hurricane Center gave 98L two-day and five-day odds of development of 60% and 70%, respectively.

Edouard Tropical storm Edouard is fifth named storm of 2020, earliest such Atlantic storm on record

The next name on the Atlantic list of storms is Fay. The earliest formation of the season’s “F” storm came on July 22, 2005, with Tropical Storm Franklin. It’s interesting to note that the last designation of the name Fay for an Atlantic storm, for Hurricane Fay in 2014, did not occur until October 10. So there’s a potential for having a Tropical Storm Fay occur three months earlier than that.

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Topics: Weather Extremes