Air pressure is the difference in pressure from one place to another. Air pressure always moves outward from a high or inward toward low-pressure. The bigger the difference between these two measurements, the stronger the wind will blow. Pressure is caused by the weight in the air and is measured by barometers. In general, weather will improve when pressure increases and worsen when pressure decreases.

High Pressure

High pressure areas, or highs, are shown by “H” symbols on a weather map. In a high pressure system (anticyclone), air pressure is greater than the surrounding areas. This difference in air pressure results in wind, or moving air. When the high pressure system is located over land, the weather will be typically dry and free of clouds – resulting in sunny skies. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in the Northern Hemisphere.

Low Pressure

Low pressure areas, or lows, are shown by “L” symbols on a weather map. A low pressure system (cyclone) develops where relatively warm air rises from the Earth’s surface. As the rising air cools, clouds will begin to form. As winds blow into a low, the air moves up. This upward flow of air can cause clouds and precipitation (usually rain) to form. Winds tend to blow into low pressure areas in an anti-clockwise motion in the Northern Hemisphere.

The mixture of gases that surround the Earth, which becomes thinner as it reaches space. The atmosphere is divided into 5 layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Most of the weather and clouds are found in the first layer (troposphere).

Astronomy

The scientific study of matter in outer space, especially their positions, dimensions, distribution, motion, composition, energy, and evolution of planets, stars and constellations. People who study outer space are called astronomers.

Constellation

A bunch of starts that are grouped together as seen from the Earth and the solar system, which were named after animals, objects, or mythological persons. There are a total of 88 constellations, such as: The Big Dipper, The Little Dipper, Orion – to name a few.

Eclipse

Occurs when one celestial body (sun, moon, Earth, etc.) moves in front of the other, blocking the sun/moonlight partially or fully. Two types of eclipses that can occur are: solar eclipse and lunar eclipse.
A solar eclipse occurs when the moon comes between the sun and the Earth; therefore the sun appears partially or fully darkened.
A lunar eclipse occurs when the Earth comes between the sun and the moon; therefore the moon appears partially or fully darkened.

Galaxy

A cluster of gas, dust, and stars that are held together by gravity. The smallest galaxies may contain only a few hundred thousand stars, while the largest galaxies have thousands of billions of stars. Our solar system is part of the Milky Way Galaxy.

Humidity

The amount of water vapor (or moisture) in the air.

Moon

An astronomical object that orbits the Earth and is visible mostly at night, as it reflects the sunlight. The moon is approximately 384,399 km (238,854 mi.) away from the Earth. A complete moon cycle (around the Earth) takes about 29 days, 12 hours, 44 minutes.
Note: that the moon has 8 phases, namely: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, and Waning Crescent.

Orbit

The curved path of a planetary object (or artificial satellite) that circles around another object. Examples of such objects include: planets, satellites, spaceships, and other celestial bodies.

Rainbow

A curve or bow that is caused by the reflection and bending of sunlight as it passes through raindrops, during or immediately after a rain shower. In heavy rains, a double rainbow can often be seen. The sequence of rainbow colors is: Red, Orange, Yellow, Green, Blue, Indigo, and Violet.
Note: A rainbow is always seen when your back is facing the sun.

Seasons

One of the four natural divisions of the year, namely: Spring, Summer, Fall/Autumn, and Winter. Each season begins on either an equinox or a solstice – astronomical phenomena that occur in March, June, September, and December. Seasons occur because of how the Earth is tilted as it circles around the sun. However, in the Caribbean, we only experience wet or dry seasons.

Equinox

The time of year when the hours of day and night are equal. This occurs twice a year, on March 21st (Vernal Equinox, beginning of Spring) and September 22nd (Autumnal Equinox, beginning of Autumn/Fall).

Solstice

The point when the sun is at its greatest distance from the equator, resulting in unequal hours of day and night. This occurs twice a year, on June 21st (Summer Solstice, beginning of Summer) and December 21st (Winter Solstice, beginning of Winter).

Solar System

The collection of planets, their moons, comets, meteoroids, asteroids, and other exciting space material. The planets of the Solar System are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and formerly Pluto.

Star

A huge ball of gas that is held together by gravity. The center of a star is extremely hot and produces energy. Some of this energy is released as visible light, thus making the star glow. Stars come in different sizes, colors, and temperatures. Our sun is a yellow star of average temperature and size.

Sun

The closest star to Earth that is the center of our solar system. The sun is responsible for most of the Earth’s weather, even though it is 93 million miles away. It is the source of the Earth’s light and heat. The Earth takes 365 ¼ days (a full year) to completely orbit the sun.

Water Cycle

Water keeps going around and around in a cycle because the Earth has a limited amount of water; therefore water is always on the move. Water evaporates (rises via heating) from the oceans and other large bodies of water, condenses (comes together with other particles) in the atmosphere, precipitates (falls as rain, snow, hail, etc.) over the land and sea, before it collects and recycles back into the air again.

Climate is not the same as weather, but rather, it is the average pattern of weather for a particular region – usually taken over a 30-year time period. On the contrary, weather describes the short-term state of the atmosphere.

Climatology

Climatology is the study of climate – which includes data taken over a period of time that may indicate differences in climate patterns. Such data is helpful in short-term weather forecasts.
For example, seasonal climate conditions for July in New York might be completely different than seasonal climate conditions in July for Miami.

Climate Types

Climates can be dry, tropical, or polar.

Tropical Climates are found in areas around the equator and are most typically warm and humid – which is the main reason why the rain forests and jungles are so lush in this tropical region.

Polar Climates are opposite of Tropical Climates, in the sense that they are always cold with longer days and are found near the North & South poles.

Subtropical Climates are typically found near oceans and may be typically hot and muggy/humid or generally rainy with cooler temperatures.

Dry Climates are also known as Desert Climates and are found throughout the deserts of North America, Mexico, Asia, and Africa.

A visible collection of very fine water droplets or ice crystals suspended in the atmosphere at altitudes from just above the ground to several miles above sea level. Clouds can come in all sizes and shapes, and cover about 50% of the Earth at any given time. We would not have rain, thunderstorms, or rainbows without clouds.

Fog

Fog is somewhat like a cloud that doesn’t take shape. It is made up of liquid water and can be called a “cloud on the ground”. Fog occurs when the air temperature matches the dew point temperature.

Cloud Types

Cloud types are classified by height and appearance. The shape depends on the way the air moves around the cloud. If the air moves horizontally, clouds form spread-out layers; while clouds grow upward if air is moving vertically near the cloud. Horizontal clouds have the suffix ‘-stratus’ and vertical clouds have the suffix ‘-cumulus’.

Cirrus

High clouds (cirrus) typically form above 23,000 feet (about 7 km or 4 miles) up in the air. Because the air is cold up there, clouds at this altitude are generally thin and formed by ice crystals. Three major types of high clouds include: cirrus, cirrocumulus, and cirrostratus. In most cases, these high clouds don’t cast shadows, are usually associated with fair weather, but may sometimes indicate that storms are on their way.

Alto

Middle layer clouds (alto) typically form anywhere between 10,000 feet (3 km or 2 miles) and 23,000 feet over the Earth. Such clouds are developed from both ice crystals and water droplets, and range between 32°F/0°C and below freezing. This type of cloud is thicker than cirrus clouds and consists mainly of two types: altocumulus and altostratus.

Stratus

Low-lying clouds (stratus) often extend from the ground to about 6,500 feet (2km or 1.5 miles) above the surface of the Earth that are typically made up of water droplets. Rain and drizzle often come from this type of cloud. The most commonly recognized low-lying clouds are: stratus, stratocumulus, and nimbostratus.

Cumulus

Cumulus clouds are big, white, fluffy cotton ball-looking clouds that have a dark and flat underside. These clouds do not hold their shape for long and typically last for less than an hour. Cumulus clouds are usually associated with fair weather, but can produce precipitation if they are very tall. When large and bunched together, they can cause heavy showers, especially in warm weather. Cumulus clouds often reach their greatest heights by late afternoon.

Nimbus

Nimbus clouds are rain-producing clouds, which are categorized by nimbostratus and cumulonimbus.
Nimbostratus clouds are very low-hanging rain clouds which blot out the sun, and are followed by lengthy precipitation within a few hours.
Cumulonimbus clouds are the most dramatic of clouds, distinguished by great vertical development and a tendency to produce rain, sleet, hail, thunder, lightning and tornadoes. The top of the cloud is often anvil-shaped.

Precipitation

Different kinds of precipitation that come from clouds are: drizzle, rain, hail, snow, sleet, and freezing rain — depending on the atmosphere’s temperature.

Haze or Mist

Haze (also known as mist) is reduced visibility in the air as a result of abundant water vapor, dust, smoke, etc. near or in contact with the Earth. Although it is invisible to the naked eye, the particles reduce visibility by being sufficiently numerous to give the air an opalescent (unclear) appearance.

Contrails

Contrails (short for “condensation trails”) are artificial clouds produced by aircraft exhaust. Contrail clouds are thin, high altitude clouds that formed when moisture released from jet engines turns into ice crystals.

Sky conditions consist of the overall cloud cover and chance of precipitation (rain). Cloud cover is the amount of clouds that cover the sky at any given time, and is based on observations more than calculations; while chance of rain is the possibility of rainfall over a particular area. Forecasts of cloud cover generally give an average, if no significant variations are expected. For example, if the forecast says “clear skies,” there may still be some visible cloud patches.

Mostly Sunny (or Mostly Clear)

The sky has little to no clouds, meaning 10% of the sky is covered by clouds.

Partly Sunny (or Partly Clear)

There is more sun than clouds in the sky, presently or within the forecast period.

%%%Partly Cloudy%%%

There are more clouds than sky in the sky, presently or within the forecast period. Therefore 10% to 50% of the sky is covered by clouds.

Mostly Cloudy

Most of the sky is covered by clouds, meaning 50 to 90% of the sky is covered.

Overcast

The sky is almost completely covered, if not fully covered, by clouds (90% to 100%).

A sudden shaking, rolling or sudden shock of the Earth’s surface, which are caused by waves in the Earth due to motion along a fault line or by volcanic activity. Earthquakes are also known as quakes, tremors, or temblors; and more than a million of them rattle the world each year. However, Earthquakes cannot be predicted (as yet).

Richter Scale

A measurement of an earthquake’s intensity, which is expressed in whole numbers and decimal fractions. Each whole-number increase on the scale indicates ten times the amount of shaking and 33 times the amount of energy. For example, a magnitude 5.3 might be documented as a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3.
Did you know that the energy released by a large earthquake may be equal to 10,000 times the energy of the first atomic bomb?

Seismology

The study of Earthquakes and the structure of the Earth, by both naturally and artificially generated seismic waves.

Seismic Waves

Seismic waves are the energy waves created by an impulse, such as an Earthquake or an explosion. They travel away from the epicenter, shaking buildings, structures and the Earth vertically, which cause them to move horizontally. Seismic waves may travel either along or near the Earth’s surface or through the Earth’s interior.

Seismograph

An instrument used for recording the intensity (strength) and duration of an Earthquake.

Epicenter

The epicenter is the point on the Earth’s surface directly above the source of the quake. Seismic waves are strongest at this point.

Faults & Fault Lines

A fault is an area of stress in the Earth where broken rocks slide past each other, causing a crack in the Earth’s surface.
A fault line is the surface trace of a fault — the line of intersection between the fault plane and the Earth’s surface.
Since faults do not usually consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane.

Aftershock

Aftershocks are Earthquakes that follow the largest shock of an Earthquake sequence. They are smaller than the main-shock and can continue to occur over a period of weeks, months, or years. In general, the larger the main-shock, the larger and more numerous the aftershocks, and the longer they will continue.

Geology

The study of the planet Earth, the materials it is made of, the processes that act on those materials, the products formed, and the history of the planet and its life forms since its origin.

An overflow of water onto normally dry land, due to rising water from a river, stream, or drainage ditch. Flooding can also be caused from a lengthy period of showers over a specific area – which may last days or weeks.

Flash Flood

A flood caused by heavy or excessive rainfall in a short period of time (generally less than 6 hours), with little or no advance warning. This fast-moving water rips through river beds, urban streets, or valleys sweeping everything in its path. They can occur within minutes or a few hours of excessive rainfall, or right after the failure of a dam.

Flash Flood Watch

Indicates that flash flooding is possible in or close to the watch area within 6 hours after the heavy rains have ended. Those in the affected area are urged to be ready to take action if a flash flood warning is issued or flooding is observed.

Flash Flood Warning

Is issued when flooding is expected to occur within 6 hours of heavy rainfall, therefore threatening life and/or property. Very heavy rain in a short period of time can lead to flash flooding, depending on local terrain.

A front is a boundary between two different systems of air (air masses), which usually results in stormy weather. A front generally separates a warm air mass from a cold air mass.

Cold Front

A cold front is a boundary between two air masses, where the cold air mass replaces the warmer air mass. On a weather map, it is represented by a blue line with “teeth” pointing toward the direction of movement.

Warm Front

A warm front is a boundary between two air masses, where the warmer air mass replaces the cooler air. On a weather map, it is represented by a red line with half circles pointing toward the direction of movement.

Stationary Front

A stationary front is a boundary between two air masses that more or less doesn’t move. However, some stationary fronts can wobble back and forth for several hundred miles a day. On a weather map, it is represented as an alternating warm and cold front symbol.

Occluded Front

An occluded front is a combination of two fronts that form when a cold front catches up and overtakes a warm front. On a weather map, it is represented as a purple line with “teeth” and half circles.

The scientific study of the Earth’s surface and its various climates, countries, peoples, and natural resources — including topography, climate, soil, vegetation, etc..

Cardinal Points/Directions

The four cardinal directions or points are the directions of North, East, South, and West — commonly denoted by their initials: N, E, S, W. Intermediate points between the four cardinal directions shape the points of the compass and include: North-East (NE), South-East (SE), South-West (SW), and North-West (NW).

Latitude

Lines of latitude, or parallels, circle the globe both north and south of the Equator. The Equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south. Lines of latitude are all parallel to each other, thus they are often referred to as parallels.

Longitude

Lines of longitude, or meridians, run to the east and west of the Prime Meridian. The Prime Meridian is assigned the value of 0 degrees. Meridians to the west of the prime meridian are measured in degrees west and likewise those to the east of the prime meridian in degrees east. The distance between lines of longitude is greater at the equator and smaller at the higher latitudes.

Note: St. Maarten = 18.0°N, 63.1°W | Saba = 17.6°N, 63.2°W | St. Eustatius = 17.5°N, 63.0°W

Equator

The geographic circle at 0 degrees latitude on the Earth’s surface. It is equal distance from the North and South Poles and divides the Northern Hemisphere from the Southern.

Prime Meridian

The zero meridian (0 degrees) from which the other meridians (lines of longitude) are calculated. It passes through Greenwich, England.

Time Zone

Time zones are areas of the Earth that follow the same definition of time. People used the sun to tell time back in the day, resulting in the time differing slightly from town to town. Time zones were thus introduced to help rectify the problem by setting the clocks of a region to the same general time. Although, time zones are usually centered along lines of longitude, the shapes of time zones can be quite irregular because of country boundaries.
All time zones, however, are regulated to Coordinated Universal Time (UTC) — the zone that includes London.
Note: The time zone for the Caribbean where we are located is Atlantic Standard Time or AST for short, which is four hours behind UTC (written as UTC-4).

Continent

A continent is one of several very large landmasses on Earth. The seven regions from largest in size to smallest are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
All continents together constitute less than one-third of the Earth’s surface, which means more than two-thirds of the Earth’s surface are covered with water. Additionally, two-thirds of the continental land mass is located in the Northern Hemisphere.

Ocean

The whole body of salt water which covers about 72% of the surface of the globe, also called the sea or great sea. It is divided into the following: Atlantic Ocean, Pacific Ocean, Indian Ocean, Arctic Ocean, and Antarctic Ocean.
Note: The Caribbean Sea (where we are located) is part of the Atlantic Ocean.

Northern Hemisphere

The half of the Earth that lies to the north of the equator.

Southern Hemisphere

The half of the Earth that lies to the south of the equator.

Global warming has affected numerous parts of the world in various capacities. Seas have risen, ice caps have melted, dry areas became drier, and wet areas became wetter – to name a few. These conditions cause big problems for not only plants and animals, but people as well.
Studies have shown that the Earth’s temperature has risen about 1 degree Fahrenheit in the last 100 years, due to Greenhouse gases (pollution) that keep heat from escaping.
Other effects of global warming include: more frequent and intense heat waves, droughts and storms; decreasing production of algae (due to warmer water); destroying huge forests (due to acid rain); and wildfires have almost become common (due to drier and warmer conditions).

El Niño

One of the most extreme weather patterns known worldwide is El Niño – a pattern that is generally recognized by above-average temperatures in the Pacific Ocean and atmospheric conditions. El Niño produces drastic weather changes in most areas.
For example, deserts that are typically dry will receive cold temperatures and rain; while on the other hand, heavily forested areas may experience warmer and drier temperatures than normal for the season.

La Niña

La Niña is a sort of the opposite of El Niño. During a La Niña pattern, the water in the same area (Pacific Ocean) along the equator gets colder than usual. This, too, affects weather around the globe. According to scientists, La Niña cycles generally create a more active hurricane season in the Atlantic.
Therefore, it is safe to say that El Niño conditions produce almost the complete opposite of normal expectations, while La Niña conditions make normal weather patterns worse.

A hurricane is a tropical cyclone in which the maximum sustained winds are 74mph (119km/h) or more. The term ‘hurricane’ is used for the Northern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern North Pacific Ocean; while the term ‘typhoon’ is used in the western Pacific Ocean; and ‘cyclone’ is used in the Indian Ocean.

Saffir-Simpson Scale

The Saffir-Simpson Scale is a 1 to 5 category system based on the hurricane’s intensity/strength at the indicated time. The scale is based primarily on wind speeds and includes estimates of barometric pressure and storm surge associated with each of the five categories. It is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall.

Hurricane Hunters

A brave crew of the Air Force Reserve that fly into tropical storms and hurricanes. They work for the National Oceanic and Atmospheric Administration (NOAA) and use specialized aircrafts that carry radar, sophisticated computers, and weather instruments that determine temperature, air pressure, wind speed, and wind direction inside the hurricane; and at different levels, as the devices drop through the hurricane toward the ocean. By the end of their flight mission, NOAA can warn everyone in the hurricane’s path.

Hurricane Season

Hurricane Season is the portion of the year having a relatively high incidence of hurricanes. The hurricane season in the Atlantic, Caribbean, and Gulf of Mexico runs from June 1 to November 30. The hurricane season in the Eastern Pacific basin runs from May 15 to November 30; whereas the hurricane season in the Central Pacific basin also runs from June 1 to November 30.

Names for the 2012 Hurricane Season are: Alberto | Beryl | Chris | Debby | Ernesto | Florence | Gordon | Helene | Isaac | Joyce | Kirk | Leslie | Michael | Nadine | Oscar | Patty | Rafael | Sandy | Tony | Valerie | William.

Hurricane Watch

An announcement that hurricane conditions (sustained winds of 74mph+ or 119kmph+) are possible within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.

Hurricane Warning

An announcement that hurricane conditions (sustained winds of 74mph+ or 119kmph+) are expected somewhere within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.

Eye

The center of a tropical storm or hurricane is relatively calm and usually has clear skies. Tropical cyclones (tropical storms or hurricanes) rotate in a counter-clockwise direction around the eye – which usually develops when the maximum sustained wind speeds exceed 75 mph (or 120kmph). It can range in size from as small as 5 miles (8km) to up to 60 miles (96.5km), but the average size is 20 miles (32km) across. Generally, when the eye begins to shrink in size, the storm is intensifying.

Eye Wall

The most violent activity takes place in the area immediately around the eye of a tropical cyclone. Cumulonimbus clouds, intense rainfall, and very strong winds take place within the eye wall, which is the area directly surrounding the eye.

Rip Current

Also known as rip tide or simply rip, is a strong channel of water flowing away from the shore, which can occur at any beach with breaking waves, including oceans, seas, and large lakes. It is localized, of narrow width, and its position relative to the beach can change as the wave condition changes. Therefore, the higher the waves, the stronger the current.

Storm Surge

An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal (or astronomic) high tide from the observed storm tide.

Fujiwara Effect

When two tropical cyclones (tropical storm, hurricane, or typhoon) come into contact with one another (within 900 miles of each other), they will begin to “dance” or orbit around each other, which is called the Fujiwara Effect. This is caused by the lack of steering winds in the upper atmosphere so the cyclones actually end up affecting each other.

Post-tropical Cyclone (Storm)

A storm that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. However, a post-tropical cyclone can continue carrying heavy rains and high winds. Two classes of post-tropical cyclones include: extratropical cyclones and remnant lows.

Extratropical Cyclone (Storm)

Unlike a tropical system, an extratropical storm has most of the higher winds in the upper atmosphere. It has a distinctive “front” and has cooler air towards the center of the system. An extratropical cyclone (or storm) typically moves away from the tropics and towards the poles, into cooler waters – thus losing its tropical characteristics.

Subtropical Cyclone (Storm)

Has traits of both a tropical and extratropical cyclone, so it is considered a hybrid (or crossover). As an example, a subtropical storm in hurricane season is weaker than a hurricane or a tropical storm, but exhibits hurricane/tropical storm traits. It has a warm center, but the eye is usually not very well-defined and swirling winds are far from the center. Subtropical systems usually develop into tropical storms.