After South Florida Flood, Tropical Storm Alex Finally Builds » Yale Climate Connections

It took record time, but Potential Tropical Cyclone 1 was finally upgraded to Tropical Storm Alex at 2:00 a.m. EDT Sunday. As of 11 a.m. EDT, Alex was located almost halfway between Florida and Bermuda, speeding northeast at 23 mph with sustained winds of 60 mph confirmed by an Air Force hurricane chaser mission . Winds above flight level were 89 knots (102 mph), but it appeared that these winds did not fully mix at the surface.

Approaching the Bermuda area, Alex will experience sea surface temperatures of around 26°C (79°F), about 1°C above average for early June, but still marginal for any tropical development. In addition, the wind shear will remain high (above 20 knots). Thus, any further intensification should be minimal. Alex is expected to head north from Bermuda on Monday, so its stronger right side could bring 2 to 3 inches of rain and tropical storm-force winds to the island.

Figure 1. The wind forecast for Alex released at 8 a.m. EDT on Sunday, June 5 showed tropical storm-force winds likely to sweep Bermuda on Monday. (Image credit: NOAA/NWS/NHC)

Finally realize your potential

PTC 1 was designated at 5 p.m. EDT Thursday, June 2 as a disorganized system near the northeastern tip of Mexico’s Yucatan Peninsula. A strong steering flow kept it heading towards South Florida, but strong wind shear prevented PTC 1 from forming a strong low level circulation and wrapping showers and thunderstorms (convection) around it . Throughout the path to Florida, convection from PTC 1 was concentrated towards its eastern and southern sides, downwind of the wind shear. It was only after crossing Florida on Saturday that PTC 1 was able to reach a well-defined low-level center, allowing the upgrade to Alex.

Of the 23 systems launched by the National Hurricane Center as potential tropical cyclones since that designation was introduced by the NHC in 2017, PTC 1 has taken by far the longest to reach its potential. A total of 57 hours passed between the launch of PTC 1 and its upgrade to Alex. The previous record was held by Claudette last year, which took 36 hours to go from TPC to tropical depression.

Only one potential tropical cyclone has ever dissipated without (up)grading: PTC 10 in 2017 was aborted after 48 hours of failed attempts to develop off the southeast coast.

Clean up South Florida

Before becoming Alex, PTC 1 made its mark in South Florida, affecting millions of residents with torrential rains and widespread street flooding. Tropical systems often bring heavy rains to South Florida at the start of hurricane season. In Cuba, where Paso Real de San Diego recorded 11.85 inches (301 mm) of rain, flooding killed at least three people and displaced more than 4,000, according to

Numerous cars stalled in the Miami-Fort Lauderdale area from Friday night through Saturday, and a few rescues took place, but no serious injuries were reported.

Record daily rainfall for Saturday June 4 included

6.55in Fort Lauderdale;

5.26” at Miami; and

4.52in West Palm Beach.

Miami’s two-day (June 3-4) rainfall total of 8.65″ was the heaviest two-day rainfall of any weather summer (June-August) since 10.33″ fell on the 29th and August 30, 1932. Even heavier rains occurred. with hurricanes and tropical storms in September.

CoCoRaHS stations reported outstanding two-day totals exceeding 10″ between Key Largo and Boca Raton, including 11.32″ just southwest of downtown Miami and 13.20″ in Biscayne Park. Brian McNoldy (University of Miami) reported a one-day total of 10.98″ at his home station CoCoRaHS on June 4, which happened to be that station’s 10th anniversary.

High water levels at a Miami-Dade wastewater treatment plant resulted in flows that were more than double the average daily flow, triggering a “no swimming” advisory for much of the area on Saturday. “This weather event produced rainfall and flow rates above/beyond the design of any treatment facility,” Miami-Dade Water and Sewer wrote in a statement. Tweeter.

Is Alex’s formation the harbinger of an active hurricane season?

Early season hurricane activity in the Atlantic in June and July generally has very little correlation with activity for the season as a whole – unless an early season storm occurs in the tropics (south of 23.5°N). Alex’s training happened in the Northwest Bahamas, a location that doesn’t necessarily imply an active season is ahead.

However, if we have a storm in June or July like we did in 2021 – when Hurricane Elsa formed in the tropical Atlantic in early July and then tracked into the eastern Caribbean – that would have likely a harbinger of an active hurricane season. Since 1900, only seven years have had hurricanes in the Eastern Caribbean before August 1: 1926, 1933, 1961, 1996, 2005, 2020, and 2021 (although 2020’s Hurricane Isaias was arguably just outside Caribbean, becoming a hurricane along the northern coast of the Dominican Republic on July 31, 2020). These seven years were classified as hyperactive Atlantic hurricane seasons according to NOAA’s definition: an accumulated hurricane energy (ACE index) of at least 160 units.

Is the Atlantic hurricane season starting earlier?

While this year marks the first year since 2014 that the Atlantic hasn’t had its first named storm before the official start of hurricane season on June 1, Alex’s appearance on June 5 comes well before the date. usual June 20 from the first storm of the 1991 season. -2020 climatology.

So, is the Atlantic hurricane season getting longer? Considering both the start and end of the Atlantic hurricane season, it appears to be lengthening in the region south of 30°N and east of 75°W, according to an article. from 2008 in Geophysical Research Letters published by Dr. James Kossin. from the University of Wisconsin and titled “Is the North Atlantic Hurricane Season Getting Longer? A 2016 analysis by WeatherTiger’s Dr. Ryan Truchelut also supported this idea. However, Juliana Karloski and Clark Evans of the University of Wisconsin-Milwaukee found no trend in tropical cyclone formation dates when looking across the Atlantic for the period 1979-2014.

The season is certainly departure earlier, looking at the date of formation of the first named storm of the season (Figure 2). However, the date of formation of the first hurricane of the season has not changed significantly.

Figures 2 and 3. Dates of formation of the first named Atlantic storm (top) and the first hurricane (bottom). (Image credit: Brian McNoldy and Brian McNoldy)

From a societal impact perspective, an earlier start to the season is not a big deal, as hurricanes are generally much more destructive than tropical storms. In a presentation May 9 to the 25th of the American Meteorological Societye Conference on Hurricanes and Tropical Meteorology, NHC Branch Chief Chris Landsea noted that more than 99% of hurricanes still occur during the hurricane season from June 1 to November 30 and that it is not no plans to extend the official season at this time.

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