How do people forecast hurricanes?

Question

i need to know for school..

thanx alot!!!

;))

Answer 1

By using a weather rador that is located in Morocco, Africa owned by the National Weather Station in Virginia. Theres also another one in Southern Miami.. They look at it every 48 hours if none has occured. Every 23 hours for Tropical Depression. Every 16 hours for Tropical Storm..And every 4 hours for Hurrican..Depends on how strong, wide, and where its heading to..

Answer 2

a. Hurricane tracking

Since tropical cyclones usually form far at sea and spend much of their existence over remote oceanic areas, detection and monitoring of these storms have traditionally posed serious problems to the forecaster. The advent of geostationary weather satellites has largely solved the detection problem and has improved the monitoring problem. However, the satellites are remote sensors and it is not unusual for position estimates to have errors of tens of miles or for wind speed estimates to be in error by tens of knots. Although advancements have been made using microwave imagery, it is still not possible to determine surface wind field distributions or detailed structural characteristics of tropical cyclones from present satellites. A combination of observing systems is necessary to provide the data required for accurate forecasts and warnings.

The principal sources of data in addition to weather satellites are reconnaissance aircraft, coastal radars, and measurements from ships, buoys, and land stations. Reconnaissance aircraft can measure details of a storm's structure when a tropical cyclone is within range of staging areas used by the aircraft. Theses specially instrumented aircraft provided accurate information on the storm's position and its current state of evolution. Surface winds can be measured from the aircraft using remote sensing techniques. Despite advancements of remote sensing capabilities from satellites, measurements from reconnaissance aircraft will be required for the foreseeable future to maintain the present level of accuracy for forecasts of landfalling tropical cyclones in the United States.

b. Hurricane track forecasting

The environmental flow in which the tropical cyclone is embedded is the main factor determining its track. Also important for track and intensity forecasts are the internal structure of the tropical cyclone and the interaction of this structure with its environment. Accurate prediction requires detailed measurements on scales that range from the storm's large-scale environment to its small inner core.

A recent assessment of the role of aircraft reconnaissance on tropical cyclone analysis and forecasting (Gray et al. 1991 ) concludes that center-fix aircraft reconnaissance is required for optimum short-range (0–24 h) forecasts of cyclone landfall and storm surge. Unfortunately, the present reconnaissance aircraft fleet and weather satellite information cannot provide the full three-dimensional data required for hurricane track forecasting. Omega dropwindsondes deployed from the aircraft can provide wind, temperature, and moisture information from flight level to the surface, and have been shown to have a positive impact on track forecast models. The aircraft are relatively slow, however, and the information derived from the sondes does not cover the important region above flight level. The remote-sensing satellite data are limited in accuracy and coverage, particularly at the critical middle-troposphere levels.

A tropical cyclone forecast involves the prediction of several interrelated quantities, but the fundamental element of the forecast is the future motion of the storm. Track prediction serves as the basis for forecasting other storm features, such as winds, rainfall, and storm surge, and, of course, the areas threatened. Normally, motion forecasts out to 72 h are issued every 6 h. These forecasts are based on guidance, ranging from simple climatological aids to complex dynamical and statistical–dynamical models. However, inconsistencies in quality and availability of these guidance products limit their utility. Thus tropical cyclone forecasting remains rather subjective, and forecaster skill and experience are important ingredients in the success of the forecast.

National Hurricane Center (NHC) forecast errors, the distance between a forecast and the subsequent observed position of the storm center, for the decade 1982–1991 averaged 54 (100), 104 (193), 206 (383), and 309 (573) n mi (km) for the 12-, 24-, 48-, and the 72-h forecasts, respectively. Using a combination of climatology and persistence as a basis for comparison, track forecast skill exists at time intervals out to 72 h, with the 48-h forecast showing the highest level of skill. Forecast errors show large spatial variation, averaging up to 30% greater than the mean in the central Atlantic, and up to 30% less than the mean over the Gulf of Mexico and the Caribbean Sea. These differences arise from better data availability in the latter areas, as well as from the different characteristics of hurricane motion within these areas.

A recent study shows that NHC 24-h forecast errors have declined about 14% over the past 20 years. This decline can be attributed to various factors, especially the improved ability, beginning in the early 1960s, to monitor and track these storms with satellite imagery. Recent improvements in dynamical and statistical–dynamical models used as forecast guidance have also contributed to decreased errors.

Consistent with current forecast accuracy, it is necessary to issue hurricane warnings for rather large coastal areas. Warnings issued 24 h before hurricane landfall average 300 n mi (560 km) in length. Normally, the swath of damage encompasses about one-third of the warned area, so the ratio of affected area to warned area is about one to three. In other words, approximately two-thirds of the area is, in effect, "overwarned." Such overwarning is not only costly, but also results in a loss of credibility in the warnings. The National Weather Service's Hurricane Probability Program was implemented as an attempt to quantify the uncertainty implicit in hurricane forecasts.

c. Forecasting hurricane intensity and coastal hazards

Numerical models can predict the storm surge inundation associated with a given hurricane with a reasonable degree of accuracy provided that the forecast of the hurricane's track and intensity are adequate. However, in view of the inherent inaccuracy in track forecasting, overwarning of storm surge flooding remains a problem.

Considerable improvement is needed in the understanding and prediction of tropical cyclone intensity changes. Present operational forecasts are only slightly better than objective forecasts that are based on persistence and climatology. Mean NHC absolute errors of maximum hurricane wind speed, most often based on satellite estimates for the decade 1981–1990, are 8.2 (4.2), 11.4 (5.9), 15.6 (8.0), and 19.1 (9.8) kt (m s-1) for the 12-, 24-, 48-, and 72-h forecasts, respectively. These errors are deceptively low, however, since they are heavily weighted toward the average condition where intensity changes are gradual and persistence forecasts work well. They do not reflect the occasional large misses that can occur with rapid strengthening or weakening of a storm. The inability to anticipate these changes for a storm that is less than 24 h from landfall is of great concern.

There is little skill in the prediction of hurricane-related rainfall. Areas of heavy rainfall can be monitored, however, from conventional radars along the United States coast. The prediction problem is complicated by terrain effects and uncertainties arising from the forecast of the track. Although in situ estimates by research aircraft of the precipitation distribution in a hurricane are becoming available, rainfall prediction remains rather subjective. Estimates of rainfall based on satellite imagery and numerical models appear to offer promising avenues for improvement.