Jeff Masters Weather Blog

Caribbean disturbance eyes Florida, Franklin poised to strengthen » Yale Climate Connections


A large low-pressure system moving from Central America into the western Caribbean on Friday afternoon was bringing disorganized heavy thunderstorms to western Cuba, Mexico’s Yucatan Peninsula, Belize, and Central America. This system was designated Invest 93L by the National Hurricane Center, or NHC, on Friday afternoon. Given the sprawling nature of the system and the potential for the center of circulation to be over land — specifically, the Yucatan Peninsula — development of 93L into a tropical depression or tropical storm is unlikely to occur through Sunday. However, on Monday, when 93L is predicted to enter the Yucatan Channel between Cuba and Mexico and enter the southern Gulf of Mexico, development chances ramp up.

Track forecast for 93L

Steering for 93L next week will be provided by a trough of low pressure passing to the north, which will grab the disturbance and pull it north to northeast. Because of the orientation of the upper-level winds, a weaker system will tend to track more to the northeast, resulting in a landfall Tuesday or Wednesday along the west coast of Florida. A strong and well-organized storm will tend to track more to the north, resulting in a landfall in the Florida Panhandle. In either case, a large swath of Florida Gulf Coast can expect heavy rains of two to four inches, with a higher core of heavier rains near where the center of the system tracks. Portions of the Florida Gulf Coast are under moderate drought, so flooding in these areas will be slower to occur.

Intensity forecast for 93L

Waters in the Gulf of Mexico are record-warm, near 31 degrees Celsius (88°F), so the main limiting factors for development will be dry air in the western Gulf and moderate to high wind shear. The models have varying depictions of the orientation of the upper-level trough of low pressure that will be steering and shearing the disturbance, so the amount of intensification that might occur is highly uncertain. The 12Z Friday run of the GFS model had 93L intensifying into a borderline tropical storm/category 1 hurricane hitting the Florida Panhandle on Wednesday morning, which is one of the most aggressive intensity forecasts that has been made.

In their 8 a.m. EDT Friday Tropical Weather Outlook, NHC gave the disturbance two-day and seven-day odds of development of 30% and 70%, respectively. A hurricane hunter mission is scheduled for Sunday afternoon into the system, along with a mission by the NOAA jet. The next name on the Atlantic list of storms is Idalia.

Franklin predicted to intensify into the Atlantic’s first major hurricane

Tropical Storm Franklin made landfall in the Dominican Republic on Aug. 23, bringing heavy rains of up to 330.7 mm (13.02 inches) that killed two people and left one missing, as reported in a separate Yale Climate Connections post. Passage over the mountainous terrain of Hispaniola disrupted the storm, which was meandering a few hundred miles north of Puerto Rico on Friday afternoon. As seen on satellite imagery, Franklin had an unhealthy appearance, with a low-level circulation center exposed to view by high wind shear and a limited amount of heavy thunderstorm activity. Despite this disheveled state, the Air Force Hurricane Hunters had a very rough ride into Franklin Thursday night, encountering significant turbulence and small hail (see Tweet below).

Over the weekend, wind shear is predicted to drop significantly over Franklin, and the storm is expected to strengthen over the warm ocean waters between Bermuda and the Bahamas. A trough of low pressure passing to the north will steer Franklin to the north on Sunday and Monday and then northeast on Tuesday, taking the core of the storm several hundred miles west of Bermuda. Rapid intensification into a major category 3 or stronger hurricane is expected on Monday and Tuesday, and the National Hurricane Center is predicting Franklin will peak as a category 3 hurricane with 125 mph winds.

By Wednesday, Franklin will be accelerating toward Newfoundland and gradual weakening will likely occur because of higher wind shear and cooler waters. Franklin may be a threat to make landfall in Newfoundland on Thursday.

satellite image of Typhoon Saola
Figure 1. Infrared satellite image of Typhoon Saola at 1530Z (11:30 a.m. EDT) Friday, Aug. 25, 2023. (Image credit: tropicaltidbits.com)

Saola may approach Asia as a dangerous super typhoon next week

In the western Pacific, intensifying Typhoon Saola will circle the waters east of the Philippines for the next several days, biding its time and gathering more strength before making a run for Taiwan and southeast China next week – perhaps as a super typhoon.

As of 8 a.m. EDT Friday, Saola was located several hundred miles northeast of Luzon island in the Philippines. With sustained winds of 105 mph, Saola was a category 2 equivalent on the Saffir-Simpson Scale. Saola had intensified by 40 mph in just 12 hours, more than enough to qualify as rapid intensification. Although Saola remained somewhat asymmetric on Friday, with the bulk of its showers and thunderstorms (convection) on its south side, the storm’s structure was improving notably. An area of convection west of Saola was over northwest Luzon, and squalls on the outer edge of Saola may drench parts of Luzon for several days to come.

Blocked from any rapid motion by strong ridging to its west and north, Saola will be carving out a large and somewhat unusual multiday loop. By Tuesday, after having angled hundreds of miles south and then back north, Saola may again be close to its Friday position. Saola’s current rapid strengthening may level off in a day or two, especially as it heads back north over cooler waters it has upwelled; we can also expect one or more eyewall-replacement cycles, which can briefly dent a typhoon’s strength. Still, Saola will likely be a formidable typhoon when it completes its loop. By that point, an upper low over far eastern Russia is predicted to accelerate Saola toward Taiwan and/or the coast of China. Aside from upwelling, Saola will remain over sea surface temperatures of 29-30 degrees Celsius (84-86 degrees Fahrenheit) over the next few days, with substantial deep-ocean heat content (see Figure 2), and wind shear should remain light to moderate (5-15 knots).

a map shows warm waters off the coast of China
Figure 2. Oceanic heat content beneath the forecast track of Typhoon Saola, in joules per square meter. Values of around 75 J/m2 or higher tend to support rapid intensification if other supportive factors are also in place. (Image credit: CIMSS/SSEC/University of Wisconsin-Madison)

The Joint Typhoon Warning Center predicted on Friday morning that Saola would be a super typhoon with top sustained winds of 150 mph as it accelerates toward Asia by midweek. Given the highly supportive conditions, a surge to category 5 strength at some point in Saola’s life cycle cannot be ruled out. Whether Saola strikes Taiwan will depend in part on potential interaction with a new typhoon expected to form to its east by early next week.

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