Prior Weather Linked to Rapid Intensification of Hurricanes Near Landfall
New study results show that ocean heat waves can provide enough fuel for hurricanes to gain momentum as they approach land.
Although most hurricanes tend to weaken as they approach
land, some rapidly increase in strength just prior to landfall - a phenomenon
that is both dangerous and hard to forecast. As the climate continues to warm,
the number of storms that fall into the latter category is likely to increase,
presenting a stark reality for communities in their paths. Because current weather
models can't accurately predict this sudden intensification, communities preparing
for a lesser storm often don't have time to respond to the arrival of a much
stronger one or to the magnitude of destruction it is likely to leave behind.
The good news? The results of a new study published
in September in Nature Communications
identify pre-storm conditions that can contribute to this rapid intensification
- an important step in improving our ability to forecast it.
"We analyzed the events that led up to Hurricane
Michael in 2018 and found that the storm was preceded by a marine heat wave, an
area of the coastal ocean water that had become abnormally warm," said
Severine Fournier, a NASA Jet Propulsion Laboratory scientist and a co-author of
the study. "Marine heat waves like this one can form in areas that have
experienced back-to-back severe weather events in a short period of time."
In October 2018, Hurricane Michael intensified from a Category
2 to a Category 5 storm the day before it made landfall in the Florida
Panhandle. Michael is the most intense storm on record to hit the area, having
left some $25 billion in damage in its wake. Using a combination of data
gathered from weather buoys and satellites, the science team behind the study examined
ocean conditions before, during, and after the hurricane.
This map of the Gulf of Mexico shows areas with unusually high sea surface temperatures before Hurricane Michael. The area from land down to the green line, and the small, enclosed areas below the green line experienced an extreme ocean heat wave in this period. The smaller circles show the path of Tropical Storm Gordon (TS), which preceded Michael; larger, darker circles show Michael's track and intensification. The legend's first four icons mark data stations. Image Credit: NASA/JPL-Caltech/University of South Alabama/DISL
› Larger view
About a month before the hurricane arrived, Tropical Storm
Gordon moved through the Gulf of Mexico. Under normal circumstances, a tropical
storm or hurricane - Gordon, in this case - mixes the ocean water over which it
travels, bringing up the cold water that is deeper in the water column to the
surface and pushing the warm surface water down toward the bottom. This newly
present colder water at the surface typically causes the storm to weaken.
But Tropical Storm Gordon was immediately followed by a
severe atmospheric heat wave during which the warm air heated the cooler ocean
water that had recently been brought to the surface. This, combined with the warm
water that Gordon had pushed down through the water column, ultimately produced
plenty of warm-water fuel for an incoming hurricane.
"In that situation, basically the whole water column
was made up of warm water," said Fournier. "So when the second storm
- Hurricane Michael - moved in, the water it brought up during mixing was warm
just like the surface water being pushed down. Hurricanes feed off the heat of
the ocean, so this sequence of weather events created conditions that were ideal
for hurricane intensification."
Although the study focuses in-depth on Hurricane Michael,
the scientists note that the pattern of weather events leading up to a major
storm - and the resulting storm intensification - doesn't appear to be unique
to Michael.
"Both Hurricane Laura and Hurricane Sally, which
impacted the U.S. Gulf Coast in 2020, appeared to have similar setups to
Michael, with both storms being preceded by smaller storms [Hurricane Hanna and
Hurricane Marco, respectively]," said lead author Brian Dzwonkowski of the
University of South Alabama/Dauphin Island Sea Lab. "Combined with warmer-than-average
summer conditions in the region, this pre-storm setup of the oceanic
environment likely contributed to those intensifications prior to landfall as
well."
NASA scientists have been tackling the question of what
causes hurricanes to intensify rapidly just before landfall from multiple
angles. Another recent
study led by JPL's Hui Su found that other factors, including the rainfall
rate inside a hurricane, are also good indicators that can help forecast if and
how much a hurricane is likely to intensify in the hours that follow. Both studies
bring us closer to understanding and being better able to forecast rapid
intensification of hurricanes near landfall.
|
