Dr. Jerry Jarrell, Chief Director of the Tropical Prediction Center in Miami, Florida is addressing a public audience concerning the current status of research into rapidly developing hurricanes. He will give the report in “layman’s” terms so as to better inform the public of the information that is available.
Hello, My name is Dr. Jerry Jarrell, Chief Director of the Tropical Prediction Center in Miami, Florida. I am here to present in layman’s terms, the current status of research into rapidly developing hurricanes. My goal is to inform you about information that is available.
The object of my status report today is to give you an update on a particular area of research being done by the Tropical Prediction Center (known as the TPC). Specifically, the occasional problem of Gulf of Mexico hurricanes rapidly and unexpectedly intensifying shortly before landfall. As a part of this update, I will explain how satellite mapping is used to aid our research.
The TPC’s goal is to better predict why and when these sudden intensifications will occur and therefore better warn coastal residents of the danger related to that particular hurricane. In a broader sense, this research is tied to a larger effort to reduce the overall costs of hurricane preparation efforts in areas that are warned but receive little or no damage. The more we can determine about how hurricanes work, the better we can pinpoint the area of potential damage and the severity.
Our primary case study is Hurricane Opal from 1995 that caused tremendous damage in Florida and Alabama in early October. During one overnight period, as shown here, **VISUAL AID #1** the Hurricane suddenly and unexpectedly strengthened from a strong Category 2 to a medium Category 4 on the Saffir-Simpson scale (a scale that meteorologists use to predict the strength of hurricanes as they make landfall.)
During this time, the windspeed increased from 110 MPH to 145 MPH and the barometric pressure decreased from 28.57 to 27.13. Because of this rapid increase, the Tropical Prediction Center was forced to broaden the warning area and recommend a greater number of coastal residents speed their precautionary measures.
Why did this happen? Hurricane Opal passed directly over what’s known as a Warm Core Eddy (or WCE). **VISUAL AID #2** Warm Core Eddies in the Gulf of Mexico are like big puddles of warm water circulating clockwise that are formed by the Loop Current, a stream of water from the Caribbean that enters the gulf through the Yucatan Channel, flows north along the west coast of Florida, then turns clockwise and flows south, exiting through the Straits of Florida. About once or twice each year a meander of the Loop Current pinches off, forming an eddy roughly 30 to 150 miles diameter and more than ˝ mile deep. Eddies travel west across the gulf as they rotate clockwise, completing a rotation about once every ten days. It takes a few months to a year for an eddy to reach the coast of Mexico or Texas in the western gulf.
Our new tool that is being used to locate these WCEs is a satellite known as TOPEX/Poseidon - which is able to determine sea heat content and locate an area of isolated warmer waters at and just below the surface of the sea. Measurements taken by the satellite taken before and after the passage of Opal over the WCE (and confirmed by sea buoy readings) show that the depth of water with temps over 68 degrees decreased by 25%. This decrease is attributed to the upwelling affect of the hurricane ”stealing” heat from the sea to fuel further storm development. TOPEX/Poseidon is now a standard tool in hurricane forecasting within the Atlantic basin - which is the source of all US hurricanes.
Now for a little information on how TOPEX/Poseidon works…
**VISUAL AID #3** - ad-lib info on picture -
The TOPEX/Poseidon satellite sends a radar beam down to the ocean’s surface and the distance it travels over time down and back up to the satellite determines the level of the ocean at any location. Another name for this is satellite altimetry. From a knowledge of the ocean topography, scientists can use a complicated formula to calculate the speed and direction of ocean current and how they change over time. When waters become cold, they begin to sink. Conversely when they become warm they rise. Factors that must also be considered are the rise and fall of the tides, the topography of the ocean bottom, and the salt content of the water. The main feature of the satellite altimetry data is the ability to detect a change over time in the depth of the ocean and the flow of ocean currents. This information is compiled to locate with a high level of precision the location of WCEs in the Gulf of Mexico. It takes approximately 10 days to map all the Earth’s oceans. The cycle repeats continuously on a 10 day cycle.
In conclusion, The TPC recommends that the TOPEX/Poseidon Satellite system be continued to be used to predict the locations of WCEs. When a hurricane is forecast to pass through one of these areas, warnings should be scaled upward to predict a larger area of severe damage - due to increased wind speed and storm surge at time of landfall. In addition, the TPS has recommended that both satellite and buoy technology be constantly examined and improved to provide more accurate results. Adding a second satellite would cut the cycle time for mapping the world’s oceans to 5 days - a shorter time frame would increase the accuracy of finding WCEs in the Gulf as a hurricane approaches landfall.
There is also no substitute for reliable communications between marine craft and land-based meteorologists for existing oceanic conditions.
