Over the course of Hurricane Irma, we received several questions regarding all aspects of the storm. Hurricane experts Dr. Erika Navarro and Dr. Rick Knabb have the answers.
Dr. Erika Navarro
Why can’t we just change the scale to include a category 6, and maybe even a 7? – Jared J.
The Saffir-Simpson scale is designed to measure the potential damage by a hurricane. Since a Category 5 storm already exhibits catastrophic damage, there is no need for a higher category.
Is it possible for 2 hurricanes to combine into 1 superstorm, or would they tear each other apart? – James L.
It is possible for two hurricanes to combine during a process called the “Fujiwhara effect.” When two cyclones are close enough together, they will begin to rotate around each other as their wind fields interact. Often, one storm will ingest the other, and only one storm will remain.
Has any meteorologist or scientist ever been able to see what’s going on beneath the surface of the ocean within the eye of the hurricane? Is there a submarine or a water vessel that is able to penetrate the center of a hurricane below the surface of the water? – Travis B.
Scientists often use satellite and ocean observations from buoys to infer details about the surface of the ocean. The ocean heat content, or the energy stored underneath the surface of the ocean, for example, can be inferred from surface measurements. Oceanographic instruments can also be deployed from aircraft, which activate when reaching the ocean surface and relay information back to the aircraft.
Did the tides affect the storm surge of the hurricane on one side of Florida more than another as far as the storm? Since the oceans and Gulf of Mexico have a big slosh factor, does the rising and falling of the tides at all affect the actual track of a hurricane? – Kim S.
The tides do not affect the track of the hurricane, but they have huge impacts for the storm surge. The flooding in Charleston, SC occurred during high hide, but the catastrophic flooding in Jacksonville, FL actually occurred during low tide. The maximum storm surge is exhibited when the onshore winds coincide with the high tide.
Why do hurricanes curve Northeast when they seem to spin counterclockwise? – Jim M.
Hurricanes are steered by the mid- to upper-level environmental flow. Often, storms that approach the US east coast are driven out to sea by strong westerly winds associated with the jet stream. However, a strong ridge of high pressure over the eastern Atlantic (and the lack of a strong jet stream dip on the US east coast) can drive storms into the Caribbean of the Gulf of Mexico.
Besides the obvious, what is the difference between a hurricane and tornado? Could one say that a tornado is basically a scaled down version of a hurricane or are they just too different to be able to compare? – Chris W.
Hurricanes and tornadoes form by very different internal processes, and differ in terms of their scale. Hurricanes are hundreds of miles across, while tornadoes at their largest can be a mile across. Despite their differences, the wind damage caused by a hurricane can be compared to that of tornado.
Why do hurricanes move so slow, and why do supercells end up moving so quickly? In fact, how do they move at all? Is it the fronts? – James M.
Hurricanes are driven by the mid- and upper-level steering, which is weaker in the tropics. Supercells are driven by vertical wind shear in the strong westerly winds associated with the jet stream.
How does Hurricane Irma compare to Hurricane Hugo in 1989? – Joseph E.
Both were at category 4 intensity at initial U.S. landfall and both inflicted tremendous storm surge and wind damage. They took very different tracks, however, with Irma making landfall in Florida going much farther south and west than Hugo than made landfall in South Carolina. However, Irma still caused some water impacts in South Carolina due to both heavy rainfall and some storm surge associated with the outermost bands when Irma had weakened to a tropical storm.
I was wondering if massive wildfires affect low and high pressure in areas and if so how might these effects impacted Hurricane Irma? – Jeremy M.
The wildfires did not have enough impact on the high and low pressure systems that steered Irma, but they can have more local pressure and wind effects in the region in which they occur.
Why is it that hurricane Harvey stopped over Houston for so long but Hurricane Irma hit Florida and kept moving upward? – Erica B.
Harvey was blocked from continuing to move north, after initial landfall in Texas, by a ridge of high pressure over the central United States that persisted for several days. Irma, however, was steered north and steadily moved over Florida in between a ridge of high pressure over the Atlantic and a low over the Gulf of Mexico and southern U.S. Right now, Hurricane Jose currently over the western Atlantic between Bermuda and Puerto Rico is being blocked from moving north by high pressure to its north. Good thing that slow motion is happening over the ocean instead of behaving like Harvey over land!
Why did Irma turn north so sharply? What was the driving force behind that turn? – Kaleb B.
Irma turned north when it reached the western edge of the ridge of high pressure over the western Atlantic, and moved north in between that ridge and a low over the Gulf of Mexico and southern U.S.
Please explain the “mb” number for a hurricane. Is it more severe if that number is lower or higher? – Cindy Sager
Pressure in the atmosphere – essentially depending on the total weight of air above the surface of the ocean or ground – is measured in millibars, with the abbreviation being “mb”. The lower the pressure inside a hurricane, the greater the difference in pressure between the inside and outside of the hurricane, and therefore the stronger the winds that are swirling around the hurricane, because winds blow as a result of pressure differences as the atmosphere tries to fill in the low pressure with air of higher pressure – kind of like a rock rolling down a hill.
What does a major hurricane do to special environments like the everglades? – John Aston
Major hurricanes like Irma that pass near or over South Florida cause storm surge, pushing the salt water from the Gulf of Mexico and fresh water from Florida Bay into portions of the Everglades. This contributes temporarily to an even greater mix of salt water and fresh water that already exists in the area, but there could be longer-term effects of Irma on the Everglades, but it is too soon to know the severity.
How much does the wind speed decrease at different distances from the eye of a hurricane? – David Doerges
The maximum winds in a hurricane are usually present in the eyewall, a solid ring of wind and rain anywhere from just a few to tens of miles from the exact center of the eye. Outside of that “radius of maximum winds” or “RMW”, hurricane-force winds can extend up to about another 100 miles or so in large hurricanes, and winds of tropical storm force can extend up to a few hundred miles more from the center, like they did in Irma when it was over Florida and, while having weakened, became larger.