Gamma (2020)

Gamma formed from a tropical wave that moved into the western Caribbean and became a tropical depression at 0600 UTC on 2 October 2020 about 260 nautical miles southeast of Cozumel, Mexico. It strengthened to a tropical storm by 1800 UTC that day and moved northwest across the northwestern Caribbean. Gamma underwent rapid intensification on 3 October and reached hurricane strength just before making landfall on the Yucatán Peninsula. After crossing the peninsula it emerged into the southern Gulf of Mexico, weakened, moved erratically while interacting with nearby Hurricane Delta, turned back toward the Yucatán, and dissipated over the peninsula by 1800 UTC on 6 October.

Gamma made two documented landfalls on the Yucatán Peninsula. The first and strongest landfall was near Tulum, Quintana Roo at 1645 UTC on 3 October as a hurricane. A later landfall as a tropical depression occurred near Nichilí (San Felipe area / northern Yucatán) around 0300 UTC on 6 October as the circulation was weakening and then dissipated over the peninsula later that day.

The storm’s maximum intensity was estimated at 65 kt (75 mph), with a minimum central pressure around 978–979 mb at the time of the Tulum landfall, making it a Category 1 hurricane at peak. Post-storm analysis of aircraft and surface observations supported the 65 kt peak intensity reached just before and at landfall on 3 October.

Gamma produced locally significant rainfall and some coastal inundation. Rainfall totals included 15.11 inches (383.8 mm) at Tizimín, 13.27 inches (337.0 mm) at Conkal, and 11.51 inches (292.3 mm) at Cozumel. Xel-Ha Park (near Tulum) reported sustained winds to 53 kt with a gust to 59 kt and measured sea-level pressures near 980–981 mb during landfall. Mexican authorities did not report significant widespread storm surge measurements, though some local inundation near the landfall area was likely.

The storm’s flooding and landslides caused six direct fatalities in Mexico: four people were killed in a Chiapas landslide that buried a home, and two people drowned in floodwaters in Tabasco. Thousands were evacuated to shelters (about 3,400 reported in Tabasco). No monetary damage estimates were available in the NHC report at the time of writing.

Noteworthy items: Gamma intensified rapidly less than 24 hours before first landfall, a change that was not anticipated in NHC operational intensity forecasts. The storm had a relatively small core so hurricane-force winds were not widely reported at land sites despite the hurricane classification. Track forecasts were near or slightly larger than average early on but comparable at longer ranges; intensity forecasts underperformed guidance beyond 12 hours, largely because they did not capture the rapid intensification and later the faster-than-expected weakening due to wind shear, dry air, land interaction, and interaction with approaching Hurricane Delta.