Tropical cyclone rainfall forecasting involves using scientific models and other tools to predict the precipitation expected in tropical cyclones A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic such as hurricanes and typhoons. Knowledge of tropical cyclone rainfall climatology A tropical cyclone rainfall climatology is developed to determine rainfall characteristics of past tropical cyclones. A tropical cyclone rainfall climatology can be used to help forecast current or upcoming tropical cyclone impacts. The degree of a tropical cyclone rainfall impact depends upon speed of movement, storm size, and degree of vertical is helpful in the determination of a tropical cyclone rainfall forecast. More rainfall falls in advance of the center of the cyclone than in its wake. The heaviest rainfall falls within its central dense overcast and eyewall The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather of a cyclone occurs. The cyclone's lowest barometric pressure occurs in the. Slow moving tropical cyclones, like Hurricane Danny (1997) Hurricane Danny was the only hurricane to make landfall in the United States during the 1997 Atlantic hurricane season, and the second hurricane and fourth tropical storm of the season. The system became the earliest 5th tropical or subtropical storm of the Atlantic season when it reached tropical storm strength on July 17, and held that record and Hurricane Wilma Hurricane Wilma was the most intense hurricane ever recorded in the Atlantic basin. Wilma was the twenty-second storm , thirteenth hurricane, sixth major hurricane, and fourth Category 5 hurricane of the record-breaking 2005 season, can lead to the highest rainfall amounts due to prolonged heavy rains over a specific location. However, vertical wind shear Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere. Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across fronts and near the coast, and vertical shear typically near the surface, leads to decreased rainfall amounts, as rainfall is favored downshear and slightly left of the center and the upshear side is left devoid of rainfall. The presence of hills or mountains near the coast, as is the case across much of Mexico In Pre-Columbian Mesoamerica many cultures matured into advanced civilizations such as the Olmec, the Toltec, the Teotihuacan, the Zapotec, the Maya and the Aztec before the first contact with Europeans. In 1521, Spain conquered and colonized the territory, which was administered as the viceroyalty of New Spain which would eventually become Mexico, Haiti Haiti (pronounced /ˈheɪti/ ; French Haïti, pronounced: [a.iti]; Haitian Creole: Ayiti, Haitian Creole pronunciation: [ajiti]), officially the Republic of Haiti (République d'Haïti ; Repiblik Ayiti) is a Caribbean country. Along with the Dominican Republic, it occupies the island of Hispaniola, in the Greater Antillean archipelago. Ayiti (land, the Dominican Republic Inhabited by Taínos since the 7th century, the territory of the Dominican Republic was reached by Christopher Columbus in 1492 and became the site of the first permanent European settlement in the Americas, namely Santo Domingo, the country's capital and Spain's first capital in the New World. In Santo Domingo stand, among other firsts in the, much of Central America Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. Central America is considered to be part of the Mesoamerican biodiversity hotspot, excluding the southern portions of Panama, Madagascar Madagascar, or Republic of Madagascar , is an island nation in the Indian Ocean off the southeastern coast of Africa. The main island, also called Madagascar, is the fourth-largest island in the world, Réunion Réunion (French: La Réunion, IPA: [la ʁeynjɔ̃] ; previously Île Bourbon) is a French island of about 800,000 population located in the Indian Ocean, east of Madagascar, about 200 kilometres (120 mi) south west of Mauritius, the nearest island. Since August 2010, the Pitons, Cirques and Remparts of the island, covering more than 40% of its, China China is seen variously as an ancient civilization extending over a large area in East Asia, a nation and/or a multinational entity, and Japan Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters that make up Japan's name mean "sun-origin", which is why Japan is act to magnify amounts on their windward side due to forced ascent causing heavy rainfall in the mountains. A strong system moving through the mid latitudes, such as a cold front The cooler, denser air wedges under the less dense warmer air, lifting it, which can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. This upward motion causes lowered pressure along the cold front. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of, can lead to high amounts from tropical systems, occurring well in advance of its center. Movement of a tropical cyclone over cool water will also limit its rainfall potential. A combination of factors can lead to exceptionally high rainfall amounts, as was seen during Hurricane Mitch Hurricane Mitch was the most powerful hurricane of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. At the time, Hurricane Mitch was the strongest Atlantic hurricane observed in the month of October, though it has in Central America Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. Central America is considered to be part of the Mesoamerican biodiversity hotspot, excluding the southern portions of Panama.^[1]

Use of forecast models can help determine the magnitude and pattern of the rainfall expected. Climatology Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences. Basic knowledge of climate can be used within shorter term weather forecasting using analog techniques such as the El Niño - Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), and persistence models, such as r-CLIPER, can create a baseline for tropical cyclone rainfall forecast skill Skill in forecasting is a scaled representation of forecast error that relates the forecast accuracy of a particular forecast model to some reference model. Simplified forecast models, such as the Kraft technique and the eight and sixteen-inch rules, can create quick and simple rainfall forecasts, but come with a variety of assumptions which may not be true, such as assuming average forward motion, average storm size, and a knowledge of the rainfall observing network the tropical cyclone is moving towards. The forecast method of TRaP assumes that the rainfall structure the tropical cyclone currently has changes little over the next 24 hours. The global forecast model which shows the most skill in forecasting tropical cyclone-related rainfall in the United States ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language is the GFS (Global Forecasting System).

Rainfall distribution around a tropical cyclone

A larger proportion of rainfall falls in advance of the center (or eye Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement. In higher organisms complex neural pathways exist that connect the eye, via the optic nerve to the visual cortex and other areas of the brain. Complex optical systems with resolving) than after the center's passage, with the highest percentage falling in the right-front quadrant A Cartesian coordinate system specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances from the point to two fixed perpendicular directed lines, measured in the same unit of length. A tropical cyclone's highest rainfall rates can lie in the right rear quadrant within a training (non-moving) inflow band.^[2] Rainfall is found to be strongest in their inner core, within a degree of latitude Latitude, usually denoted by the Greek letter phi gives the location of a place on Earth (or other planetary body) north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west (or west to east) on maps (particularly so in the Mercator projection) that run either north or south of the equator of the center, with lesser amounts farther away from the center. Most of the rainfall in hurricanes is concentrated within its radius of gale-force winds The Beaufort Scale is an empirical measure for describing wind speed based mainly on observed sea conditions. Its full name is the Beaufort Wind Force Scale.^[3] Larger tropical cyclones have larger rain shields, which can lead to higher rainfall amounts farther from the cyclone's center.^[3] Storms which have moved slowly, or loop, lead to the highest rainfall amounts. Riehl calculated that 33.97 inches (863 mm) of rainfall per day can be expected within one-half degree, or 35 miles (56 km), of the center of a mature tropical cyclone.^[4] Many tropical cyclones progress at a forward motion of 10 knots, which would limit the duration of this excessive rainfall to around one-quarter of a day, which would yield about 8.50 inches (216 mm) of rainfall. This would be true over water, within 100 miles (160 km) of the coastline,^[5] and outside topographic features. As a cyclone moves farther inland and is cut off from its supply of warmth and moisture (the ocean), rainfall amounts from tropical cyclones and their remains decrease quickly.^[6]

Vertical wind shear

Vertical wind shear Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere. Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across fronts and near the coast, and vertical shear typically near the surface, forces the rainfall pattern around a tropical cyclone to become highly asymmetric, with most of the precipitation falling to the left and downwind of the shear vector, or downshear left. In other words, southwesterly shear forces the bulk of the rainfall north-northeast of the center.^[7] If the wind shear is strong enough, the bulk of the rainfall will move away from the center leading to what is known as an exposed circulation center. When this occurs, the potential magnitude of rainfall with the tropical cyclone will be significantly reduced.

Interaction with frontal boundaries and upper level troughs

As a tropical cyclone A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic interacts with an upper-level trough A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts and the related surface front Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations. Weather maps are created by plotting or tracing the values of relevant quantities such as sea level pressure, temperature, and cloud cover onto a, a distinct northern area of precipitation is seen along the front ahead of the axis of the upper level trough. Surface fronts with precipitable water amounts of 1.46 inches (37 mm) or more and upper level divergence overhead east of an upper level trough can lead to significant rainfall.^[8] This type of interaction can lead to the appearance of the heaviest rainfall falling along and to the left of the tropical cyclone track, with the precipitation streaking hundreds of miles or kilometers downwind from the tropical cyclone.^[9]

Mountains

Moist air forced up the slopes of coastal hills and mountain chains can lead to much heavier rainfall than in the coastal plain.^[10] This heavy rainfall can lead to landslides, which still cause significant loss of life such as seen during Hurricane Mitch Hurricane Mitch was the most powerful hurricane of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. At the time, Hurricane Mitch was the strongest Atlantic hurricane observed in the month of October, though it has in Central America Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. Central America is considered to be part of the Mesoamerican biodiversity hotspot, excluding the southern portions of Panama, where several thousancd perished.^[11]

Tools used in preparation of forecast

Climatology and persistence

The Hurricane Research Division of the Atlantic Oceanographic and Meteorological Laboratory The Atlantic Oceanographic and Meteorological Laboratory is a laboratory in National Oceanic and Atmospheric Administration's Office of Oceanic and Atmospheric Research (OAR) created the r-CLIPER (rainfall Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface. On Earth, it is the condensation of atmospheric water vapor into drops of water heavy climatology Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences. Basic knowledge of climate can be used within shorter term weather forecasting using analog techniques such as the El Niño - Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), and persistence) model to act as a baseline for all verification regarding tropical cyclone A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic rainfall. The theory is, if the global forecast models cannot beat predictions based on climatology, then there is no skill Skill in forecasting is a scaled representation of forecast error that relates the forecast accuracy of a particular forecast model to some reference model in their use. There is a definite advantage to using the forecast track with r-CLIPER because it could be run out 120 hours/5 days with the forecast track of any tropical cyclone globally within a short amount of time.^[12] The short range variation which uses persistence is the Tropical Rainfall Potential technique (TRaP) technique, which uses satellite-derived rainfall amounts from microwave Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band ( imaging satellites The first satellite photographs of Earth were made on August 14, 1959 by the U.S. satellite Explorer 6. The first satellite photographs of the Moon might have been made on October 6, 1959 by the Soviet satellite Luna 3, on a mission to photograph the far side of the Moon. The Blue Marble photograph was taken from space in 1972, and has become very and extrapolates the current rainfall configuration forward for 24 hours along the current forecast track.^[13] This technique's main flaw is that it assumes a steady state The concept of steady state has relevance in many fields, in particular thermodynamics and economics. Steady state is a more general situation than dynamic equilibrium. If a system is in steady state, then the recently observed behavior of the system will continue into the future. In stochastic systems, the probabilities that various different tropical cyclone which undergoes little structural change with time, which is why it is only run forward for 24 hours into the future.^[14]

Numerical weather prediction

Computer models can be used to diagnose the magnitude of tropical cyclone rainfall. Since forecast models output their information on a grid, they only give a general idea as to the areal coverage of moderate to heavy rainfall. No current forecast models run at a small enough grid scale (1 km or smaller) to able to detect the absolute maxima measured within tropical cyclones. Of the United States ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language forecasting models, the best performing model for tropical cyclone rainfall forecasting is known as the GFS, or Global Forecasting System.^[15] The GFDL The Geophysical Fluid Dynamics Laboratory is a laboratory in the National Oceanic and Atmospheric Administration (NOAA)/Office of Oceanic and Atmospheric Research (OAR). The current director is Dr. V. Ramaswamy model has been shown to have a high bias concerning the magnitude of heavier core rains within tropical cyclones.^[16] Beginning in 2007, the NCEP The United States National Centers for Environmental Prediction delivers national and global weather, water, climate and space weather guidance, forecasts, warnings and analyses to its Partners and External User Communities. These products and services are based on a service-science legacy and respond to user needs to protect life and property, Hurricane-WRF became available to help predict rainfall from tropical cyclones.^[17] Recent verification shows that both the European ECMWF forecast model and North American Mesoscale Model (NAM) show a low bias with heavier rainfall amounts within tropical cyclones.^[18]

Kraft rule

During the late 1950s, this rule of thumb A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. Compare this to heuristic, a similar concept used in mathematical discourse, came into being, developed by R. H. Kraft.^[19] It was noted from rainfall amounts (in imperial units) reported by the first order rainfall network in the United States ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language that the storm total rainfall fit a simple equation: 100 divided by the speed of motion in knots.^[9] This rule works, even in other countries, as long as a tropical cyclone is moving and only the first order or synoptic station network (with observations spaced about 60 miles (97 km) apart) are used to derive storm totals. Canada uses a modified version of the Kraft rule which divides the results by a factor of two, which takes into account the lower sea surface temperatures seen around Atlantic Canada and the prevalence of systems undergoing vertical wind shear at their northerly latitudes.^[18] The main problem with this rule is that the rainfall observing network is denser than either the synoptic reporting network or the first order station networks, which means the absolute maximum is likely to be underestimated. Another problem is that it does not take the size of the tropical cyclone or topography into account.

See also

• Tropical cyclone forecasting Tropical cyclone forecasting is the science and art of forecasting where a tropical cyclone's center, and its effects, are expected to be at some point in the future. There are several elements to tropical cyclone forecasting: track forecasting, intensity forecasting, rainfall forecasting, storm surge, and tornado forecasting. While skill is
• Tropical cyclone observation Tropical cyclone observation has been carried out over the past couple of centuries in various ways. The passage of typhoons, hurricanes, as well as other tropical cyclones have been detected by word of mouth from sailors recently coming to port or by radio transmissions from ships at sea, from sediment deposits in near shore estuaries, to the

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