Sara vs. Helene: How 2024’s worst tropical flood events compare
Both storms produced more than 700 mm of rain, but they couldn't be more different from one another
Hundreds of millimetres of rain have fallen on Honduras as slow-moving Tropical Storm Sara spins over coastal portions of Central America.
Sara is likely going to go down as one of the region’s most prolific rainstorms in recent memory, joining this past September's Hurricane Helene to make flash floods the storm’s foremost calamity.
Here’s a look at how prolific rains during Tropical Storm Sara and Hurricane Helene each played out in their own unique way.
DON'T MISS: How Hurricane Helene produced 700+ mm of rain in three days
Tropical Storm Sara unleashes extreme flooding
Tropical Storm Sara is a classic late-season storm in the western Caribbean Sea. Warm water temperatures and favourable atmospheric conditions make this region of the Atlantic the most common place for storms to form this late in the hurricane season, which ends on Nov. 30.
The system stalled out as it approached northern Honduras. A ridge of high pressure over the northern Caribbean cut off steering winds around the storm, and the feature acted like a barrier to prevent Sara from moving north out of the region.
As a result, the storm has meandered just offshore and washed persistent rounds of drenching rains into the coast.
Northern Honduras is a highly mountainous region. These rainfall rates were enhanced by a process known as orographic lift—winds rising up the slopes of the mountains, wringing out their moisture along the way in the form of torrential downpours.
La Ceiba, which is home to a quarter of a million people, reported 732.0 mm of rain in between Nov. 14 and Nov. 16. The rain isn’t expected to stop until Sunday, and some areas in Honduras could see 700-1000 mm of rain by the time the storm finally ends this weekend.
This led to widespread flash floods and mudslides throughout the country. The full scope of the devastation won't be known for days.
Helene’s rains started long before the storm arrived
The setup that produced Tropical Storm Sara’s extensive flash flooding is much different from the scenario we saw unfold during Hurricane Helene.
Helene churned through the eastern Gulf of Mexico in late September as a powerful major hurricane that would slam into Florida with maximum sustained winds of 225 km/h.
Long before Helene hit Florida, though, drenching rains began falling hundreds of kilometres inland. This phenomenon is known as a Predecessor Rain Event (PRE).
A deep plume of tropical moisture streaming ahead of Hurricane Helene ran into a boundary parked over the interior southeastern United States. This boundary squeezed the tropical moisture out of the air like a sponge, leading to days of heavy rain across the mountainous terrain of North Carolina and Tennessee.
Only after several days of rain did the core of Helene arrive, hitting the region with a second punch of additional heavy rainfall that surged local waterways far beyond their banks. Some communities saw more than 700 mm of rain over the course of several days, pushing rivers so high that they washed away entire towns.
The two events each highlight how tropical systems are multi-faceted threats that can create a unique set of hazards. Regardless of a storm's strength, flash flooding from heavy rain is almost always the deadliest hazard with any landfalling system.