Sky Conditions

Okta
Used for the measurement of total cloud cover. One okta of cloud cover is the equivalent of 1/8 of the sky covered with cloud.
Clear Skies
No cloud cover
Fair
Cloud cover is 2 oktas or less of low and or medium clouds for most of the time with isolated light rainfall or no rainfall. Term can be used both for day and night time
Mainly Fair
Generally fair (2 oktas or less) interspersed by brief periods of partly cloudy to cloudy skies (3 oktas or more) with isolated light rainfall or no rainfall. Term can be used both for day and night time
Sunny
Cloud cover 2 oktas or less being sunny for prolonged periods with isolated light rainfall no rainfall
Partly Cloudy
Cloud cover for the greater part of the time averages 3 to 4 oktas of low and or medium clouds or dense high level clouds of 5 oktas or more, interspersed with brief periods of fair or cloudy skies. Periods of isolated light or moderate showers are likely or no rainfall
Mostly Cloudy
Cloud cover of 5 oktas or more interspersed with brief periods of fair to partly cloudy skies. Shower activity likely to be light to isolated moderate
Cloudy
Cloud cover is greater than 4 oktas and shower activity likely to be light to moderate and isolated heavy
Overcast
Cloud cover of 8 oktas and shower activity likely to be light to moderate interspersed by heavy periods
Increasingly Cloudy
Cloud cover generally increasing from fair or partly cloudy to cloudy or overcast
Decreasingly Cloudy
Cloud cover generally decreasing from overcast or cloudy to partly cloudy or fair
Showers
Precipitation, often short-lived and heavy, falling from convective or towering clouds. A shower is characterized by its sudden beginning and ending and generally by large and rapid changes of intensity
Rain
Precipitation of liquid water particles in the form of drops of more than 0.5 mm in diameter
Spatial Coverage
Isolated – Rainfall occurring across 10% or less of the forecast area
Few – rainfall occurring over 10% to 30% of the forecast area
Scattered – rainfall occurring over 30% to 60% of the forecast area
Showers (no description) – rainfall covering greater than 60% of the forecast area
Temporal Coverage
Brief – Shower event that occurred for 10 minutes or less
Periods of showers/rain – several instances of shower events throughout the forecast period

Conditions Associated with Wind

Breezy
Wind speeds averaging 12 – 18 kts (22-33 km/h)
Windy
Wind speeds averaging 19 kts (35 km/h) and higher
Low Level Jet
Wind speed in the lower levels of the atmosphere (surface-10,000ft) averaging 25kts (46 km/h) or higher
Upper Level Jet
Wind speed in the upper levels of the atmosphere of 50 kts (93 km/h) or higher
Moisture Convergence
Moisture convergence - Is the advection or transport of moisture into a fixed region such as the Lesser Antilles that usually promotes an increase in moisture levels and the potential for shower activity. Moisture advection is common along cold fronts or any other low-level boundary that causes general convergence such as the land mass of mountainous islands
Advection
Transport of water or air along with its properties (e.g. temperature, moisture) by winds or currents
Subsidence
Slow descent or sinking of a mass of air, over a wide area, generally accompanied by horizontal divergence or air moving away from a point, in the lower layers. The subsiding air is compressed and warmed usually increasing stability or lessening the potential for shower activity

Weather Systems

High Pressure System
An area of higher pressure relative to the surrounding region identified with a clockwise circulation in the northern hemisphere and a counterclockwise circulation in the southern hemisphere. Also, defined as an anticyclone
Ridge
An elongated area of relatively high pressure that is typically associated with an anti-cyclonic wind shift
Low Pressure System
An area of low pressure relative to the surrounding region identified with counter-clockwise circulation in the northern hemisphere and clockwise in the southern hemisphere. Also, defined as a cyclone
Trough
A trough is an elongated area of low pressure. Troughs develop at varying levels of the atmosphere and can be separated as:
  • Low level trough - up to 10,000ft
  • Middle level trough - up to 18000ft
  • Upper level trough - above 18000ft
Tough System
Term used to describe a trough that is manifested from the surface through to the upper levels of the atmosphere
Tropical Wave
A trough or cyclonic curvature maximum in the trade-wind easterlies. (A tropical wave may be differentiated from the normal trough based on where and how they are usually formed and their movement)
Tropical Disturbance
A discrete tropical weather system of apparently organized convection originating in the tropics or subtropics that maintain its identity for 24 hours or more
Potential Tropical Cyclone
A term used to describe a disturbance that is not yet a tropical cyclone, but which poses the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours
Tropical Depression
A tropical cyclone in which the maximum sustained surface wind speed is 33 kt (38 mph or 62 km/hr) or less
Tropical Storm
A tropical cyclone in which the maximum sustained surface wind speed ranges from 34 kt (39 mph or 63 km/hr) to 63 kt (73 mph or 118 km/hr)
Tropical Storm Watch
An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are possible within the specified area within 48 hours
Tropical Storm Warning
An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are expected somewhere within the specified area within 36 hours
Hurricane
A tropical cyclone in which the maximum sustained surface wind is 64 kt (74 mph or 119 km/hr) or more
Major Hurricane
A hurricane that is classified as Category 3 or higher
Hurricane Watch
A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous
Hurricane Warning
A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. A warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. Preparations to protect life and property should be rushed to completion
Eye
The roughly circular area of comparatively light winds that encompasses the center of a severe tropical cyclone. The eye is either completely or partially surrounded by the eyewall cloud. The eye usually experiences little or no precipitation
Rapid Intensification
An increase in the maximum sustained winds of a tropical cyclone of at least 30kt (56km/h) in a 24-hr period
Feeder Bands
Lines or bands of low-level clouds that move (feed) into the updraft region of a thunderstorm, usually from the east through south (i.e., parallel to the inflow). Same as inflow bands. This term also is used in tropical meteorology to describe spiral-shaped bands of convection surrounding, and moving toward, the center of a tropical cyclone.
Outer Convective Band
Bands in a hurricane that occur in advance of main rain shield and up to 300 miles from the eye of the hurricane. The typical hurricane has two or three bands (and sometimes more) which are comprised of cells resembling ordinary thunderstorms. Wind gusts are usually higher in these bands than in the Pre-Hurricane Squall Line.

 

Inter-Tropical Convergence Zone
A zonally elongated axis of surface wind confluence of northeasterly and southeasterly trade winds in the tropics
Fronts
The interface or transition zone between two air masses of different density. Density depends on temperature and moisture content. Fronts either lie along shear lines or can lag behind them
Shear Line
It is an area of directional wind confluence (coming together) along the tail end of a surface front or a line or narrow zone across which there is an abrupt change in the horizontal wind component parallel to this line
Flood
The term flood is generally defined as a rise in the water level of a stream or water body to a peak from which the water level recedes at a slower rate
Flash Flood
A flash flood is a sudden local flood of great volume and short duration which follows within a few (usually less than six) hours of heavy or excessive rainfall, or due to dam or levee failure. Saturated soils, steeply sloping highland terrains and narrow valleys or ravines which hasten runoff also promotes flash floods
Flood/ Flash Flood Watch
A Flash Flood Watch means that flash flooding is possible
Flood/ Flash Flood Warning
A Flash Flood Warning means that flooding is already occurring or will occur during the warning period
Small Craft Warning
A small craft Warning means that winds-speeds of 25 knots (46km/h) or higher and/or seas of 3m (10ft) or greater are forecast to affect the marine area
High Surf Advisory
A High Surf Advisory is issued when breaking wave action poses a threat to life and property within the surf zone
Marine Conditions (Waves/Swells)
Slight: 0.5 -1.3m / 1 to 4 feet
Moderate: 1.3 – 2.5m / 4 to 8 feet
Rough: 2.5 – 4m / 8 – 12 feet
Very Rough: 4.0 – 6.0m / 13 to 20 feet
High: 6.0 – 9.0m / 20 to 30 feet
Dangerous: >9.0m / 30.0 feet
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
Landslide
Generally describe the downslope movement of rock, debris or soil. Landslides can be initiated in weak or compromised slopes by heavy or prolonged rainfall, stream erosion, changes in ground water, earthquakes, volcanic activity and disturbance by human activities
Rockfall
Rock falls are abrupt, downward movements of rock or earth, or both, that detach from steep slopes or cliffs
Vigilant
Keeping careful watch, be alert, be on the lookout for deterioration in weather conditions that may affect you or create difficulties

Latitude and Longitude

Latitude lines run horizontally on a map. They are also known as parallels since they are parallel and equal distance from each other. They are almost as if stacked on top of each other. Lines or degrees of latitude are approximately 69 miles or 111 km apart, with variation due to the fact that the earth is not a perfect sphere but an oblate ellipsoid (slightly egg-shaped). To remember latitude, imagine the lines as horizontal steps of a ladder, "ladder-tude", or by the phrase "stepping on latitude". There is both a north and south set of latitude degrees that run from zero degrees (0°) to ninety degrees (90°). The equator, the imaginary line that divides the planet into a northern and southern hemisphere, represents zero (0°). The degrees increase in either direction from this marker to ninety degrees (90°) north to the North Pole and 90° south to the South Pole.
Longitude
The vertical lines on a map are called longitude lines, also known as meridians. Unlike latitude lines which are parallel, longitude lines narrow as they approach the North and South Pole. Longitude lines converge at the poles and are widest at the equator. At their widest points, these are about 69 miles or 111 km apart like latitude lines. Longitude degrees extend 180° east and 180° west from the prime meridian, an imaginary line dividing the earth into an eastern and western hemisphere, and meet to form the International Date Line in the Pacific Ocean at 180° longitude. Zero degrees (0°) longitude falls in Greenwich, England, where a physical line showing the division between the Eastern and Western hemispheres was constructed. The Royal Greenwich Observatory was established as the site of the prime meridian by an international conference in 1884 for navigational purposes.
Using Latitude and Longitude
To precisely locate points on the earth's surface, we can use latitude and longitude coordinates. Degrees are divided into sixty (60) equal parts called minutes (') and those are further divided into sixty (60) equal parts called seconds ("). Do not confuse these units of measurement with units of time. Seconds can be broken down into tenths, hundredths, or even thousandths for the most precise navigation. Degrees latitude are either north (N) or south (S) and degrees longitude are either east (E) or west (W). Coordinates can be written as DMS (degrees, minutes, and seconds) or decimals. To get decimal, you divide minute by sixty minutes. E.g. 15° 30' N equals 15° (30'/60') N. The result is 15.5° N. Example of Coordinates • Dominica is located at 15.3°N and 61.4°W.