|TEXT ONLY VERSION||NATIONAL HURRICANE CENTER|
The National Weather
Service (NWS) has several tools to monitor hurricanes. While they are still
far out in the ocean, indirect measurements using satellites are the main tool,
although ships and buoys also provide observations. Once the storms come closer
to land, more direct measurements (reconnaissance aircraft, radiosondes, and
Automated Surface Observing Stations) are also used. Within about 200 miles
of the coast, radar provide important indirect measurements of the storm.
Satellite images provide:
Basic day/night cloud imagery
Observations of land surface temperature data
Sea surface temperature data
Winds from cloud motions at several levels
Hourly cloud-top heights and amounts
Rainfall estimates for flash flood warnings
Ships and buoys provide additional information about the wind speed and direction, pressure, air and sea temperature, and wave conditions within the tropical cyclone. Ships and buoys are the only routine source of measured waves in areas unobstructed by land and are often the only way to take direct measurements when a tropical storm is still at sea. As a result, they provide observational ground truth for indirect measurements (such as satellite and radar) in the marine environment.
The most direct method of measuring the winds in the hurricane is to send reconnaissance aircraft into the storm. Those measurements are limited because they cannot be taken until the hurricane is relatively close to shore. In addition, the measurements are not taken continuously or throughout the storm, so what we have is a snapshot of small parts of the hurricane. Nonetheless, that information is critical in analyzing the current characteristics needed to forecast the future behavior of the storm.
The U.S. Air Force Reserve uses specially equipped C-130 aircraft to conduct most operational reconnaissance. Pilots fly the aircraft into the hurricane center to measure winds, pressure, temperature, and humidity, as well as to provide an accurate location of the eye.
The National Oceanic and Atmospheric Administration (NOAA) also flies aircraft into hurricanes to aid scientists in better understanding these storms and to improve forecast capabilities. The P3 Orion aircraft and state-of-the-art high altitude jet aircraft complement the U.S. Air Force Reserve's hurricane reconnaissance function.
The data provide an important vertical profile of the hurricane's environment, which is critical for forecast models. Radiosondes are generally only released over land, which leaves a large data gap over the oceans.
Dropsondes are a variation on the radiosonde. Instead of being carried aloft by a balloon, the dropsondes, which are attached to a small parachute, are dropped into the hurricane from the reconnaissance aircraft. These instruments are helping forecasters to make great strides in understanding and predicting hurricane behavior.
Sophisticated mathematical calculations give forecasters important information derived from the radar data, such as estimates of rainfall amounts. A limitation of these radars is that they cannot "see" farther than about 200 miles from the coast, and hurricane watches and warnings must be issued long before the storm comes into range.
The images above
show two important radar products used by forecasters. The reflectivity images
(above left) are the ones frequently shown on TV. In these pictures, the forecaster
can pick out details about storm features (such as the locations of the eye
and rainbands), storm motion, and intensity. The radial wind velocity product
(above right) gives forecasters important information about wind speed and direction
that was not available with the older style radars. These tools allow forecasters
to provide much more timely and accurate warnings than were possible only a
few years ago.
Automated Surface Observation System (ASOS) is located in more than 850 locations throughout the country. These monitoring systems provide forecasters with surface weather observations around the clock. However, because the systems are land-based, ASOS data is mainly useful once the hurricane has come close to shore or after it has made landfall. This information is invaluable in post-analysis.
After Hurricane Andrew (1992) the NHC and the local Miami NWS office asked the public for help with surface observations. They received over 100 responses from people who had collected data during the storm. This was invaluable in reconstructing Andrew's effects, as the normal observation network was destroyed in the hurricane.
Visit these websites to learn more