Hundreds of millimeters of rain have fallen on Honduras as slow-moving Tropical Storm Sara orbits coastal areas of Central America.
Sara will likely go down as one of the most prolific rain storms in recent memory, joining last September’s Hurricane Helene in making flash flooding the storm’s biggest disaster.
Here’s a look at how the heavy rains during Tropical Storm Sara and Hurricane Helene each played out in their own unique ways.
DON’T MISS: How Hurricane Helene produced more than 700mm of rain in three days
Tropical Storm Sara causes extreme flooding
Tropical Storm Sara is a classic late-season storm in the western Caribbean Sea. Warm water temperatures and favorable atmospheric conditions make this part of the Atlantic Ocean the most common place for storms this late in the hurricane season, which ends on November 30.
The system stalled as it approached northern Honduras. A high-pressure ridge over the northern Caribbean cut off steering winds around the storm, and the feature acted as a barrier to prevent Sara from moving the region north.
As a result, the storm has moved just offshore and persistent rain showers have washed onto the coast.
Northern Honduras is a very mountainous area. These precipitation figures were increased by a process known as orographic lift: winds rising up the slopes of the mountains, wringing out their moisture in the form of heavy downpours along the way.
La Ceiba, home to a quarter of a million people, reported 552.0 mm of rain in 24 hours between November 14 and November 15. The rain is not expected to stop anytime soon, and some areas in Honduras could see rain. 700-1000mm of rain by the time the storm finally passes this weekend.
This led to widespread flash flooding and mudslides across the country. The full extent of the destruction will not be known for days.
Helene’s rain started long before the storm arrived
The setup that led to Tropical Storm Sara’s extensive flash flooding is starkly different from the scenario we saw unfold during Hurricane Helene.
Helene tore through the eastern Gulf of Mexico in late September as a powerful major hurricane that would barrel into Florida with maximum sustained winds of 140 mph (225 km/h).
But long before Helene hit Florida, it started raining hundreds of miles inland. This phenomenon is known as a Predecessor Rain Event (PRE).
A deep plume of tropical moisture flowing ahead of Hurricane Helene hit a boundary parked over the interior of the southeastern United States. This boundary squeezed tropical moisture out of the air like a sponge, leading to days of heavy rain in the mountainous terrain of North Carolina and Tennessee.
Only after several days of rain did Helene’s core arrive, hitting the region with a second blow of additional heavy rainfall that caused local waterways to rise well beyond their banks. Some communities saw more than 700mm of rain over the course of several days, pushing rivers so high that entire towns were washed away.
The two events each highlight how tropical systems are multifaceted 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 in any landfall system.
WATCH: Comparing Hurricane Helene to B.C.’s 2021 floods
Click here to watch the video
