Above: Enhanced infrared image of the broad, disorganized zone of showers and thunderstorms associated with Invest 90L at 0036Z Friday, May 15, 2020 (8:36 pm EDT Thursday). (NASA/MSFC Earth Science Branch)
Florida’s Middle Keys were drenched on Thursday by downpours associated with Invest 90L, a disturbance that is likely to become a tropical or subtropical storm by this weekend. In a special tropical weather update issued at 8 pm EDT Thursday evening, the NOAA/NWS National Hurricane Center gave 90L a 70% chance of becoming at least a depression by Saturday night and an 80% chance by Tuesday night.
The first name on the 2020 list of Atlantic storms is Arthur.
Although this system is likely to peak in strength as it heads into the open Atlantic, it may bring more rounds of torrential rain to South Florida and parts of The Bahamas before then. By Monday, its western edge could brush the Outer Banks of North Carolina with gusty winds and squalls.
90L is gradually organizing along a diffuse frontal zone that extends from The Bahamas into the southeast Gulf of Mexico. Moisture has been pooling along this front, and a subtle upper-level impulse approaching from the west is helping to kick off showers and thunderstorms (convection) and to induce low pressure at the surface. A tiny low-level circulation was evident on satellite Thursday afternoon just south of the Keys, spinning out from beneath a canopy of disorganized but heavy convection amid strong westerly wind shear.
In the Middle Keys, Marathon recorded its second wettest May day on record and the tenth wettest day of any month, with 5.35” as of 6 pm EDT.
Outlook for 90L
For several days, computer models have given ample notice of the potential for a subtropical or tropical cyclone to develop somewhere between Florida and the Bahamas this weekend. Although some of the details remain murky, it appears that whatever forms will move generally northeast, away from U.S. shores.
Sea surface temperatures are around 27-28°C (81–82°F) off South Florida, which is more than warm enough for tropical development. Strong wind shear will continue to tap on the brakes of development into Friday. By Saturday morning, wind shear should drop into the moderate range, and 90L is expected to still be somewhere off the southeast Florida coast, close to the Northwest Bahamas. One plausible scenario is that 90L might become a tropical depression and perhaps a tropical storm on Saturday, then evolve into a subtropical storm as it journeys over cooler waters of 24–26°C (75–79°F) just off the southeast U.S. coast. As is often the case with subtropical cyclones, cold air aloft should help compensate for relatively cool SSTs in providing the instability needed for convection.
Longer-range models, especially the GFS, are suggesting that 90L could nudge within about 200 miles to the North Carolina coast around Monday, close enough for the possibility of gusty winds and perhaps a few stray squalls. The system—most likely still a subtropical storm—should then angle more eastward and head out to sea, as a sprawling cut-off low dives into the southeast U.S.
A hurricane hunter flight into 90L is tentatively scheduled for Friday afternoon.
Vongfong weakens on its trek through the Philippines
Making a series of landfalls along its way, Typhoon Vongfong (named Ambo in the Philippines) was dumping moderate to heavy rains as it pushed across the rugged terrain of the central Philippines islands on Friday local time. The Joint Typhoon Warning Center pegged Vongfong’s sustained (1-minute) winds at minimal Cat 1 strength, 75 mph, as of 18Z Thursday (2 pm EDT). According to weather.com, Vongfong’s peak winds were minimal Cat 3 strength, 115 mph, less than two hours after it made its first landfall around 12:15 pm Thursday local time.
By Friday morning local time, Vongfong had already made five landfalls, according to PAGASA, the Philippines meteorological agency: (1) San Policarpo, Eastern Samar; (2) Dalupiri, Northern Samar; (3) Capul, Northern Samar; (4) Ticao Island, Masbate; & (5) Burias Island, Masbate.
Power outages hit the provinces of Eastern and Northern Samar, the Associated Press reported. There were no immediate reports of major damage or injuries.
Vongfong will continue to churn northwestward through the largest of the Philippine islands, Luzon, as a weakening tropical storm into Saturday local time. Some flooding and mudslides will be possible. Vongfong’s structure will continue to decay from the dual impact of land interactions and increasing wind shear, though, and this could limit the worst impacts.
