HYDROLOGY


Great Lakes Marine Terms
Coastal/Oceanic Marine Terms

FLOOD TERMS

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The following advisory terms are used to ALERT the public of weather situations that are not necessarily associated with precipitation, but need to be highlighted. The warning terms are used to WARN the public of non-precipitation events that could be a threat to life and/or property.

FLOOD STATEMENT, or FLASH FLOOD STATEMENT
Flood Statement is issued to give the public follow-up information on current urban/small stream flooding, or general widespread flooding. A Flash Flood Statement is issued to inform the public about current flash flood conditions. These statements usually contain river stage information if major streams or rivers are involved.
URBAN/SMALL STREAM FLOOD ADVISORY
Alerts the public to flooding which is generally only an inconvenience (not life-threatening) to those living in the affected area. Issued when heavy rain will cause flooding of streets and low-lying places in urban areas. Also used if small rural or urban streams are expected to reach or exceed bankfull. Some damage to homes or roads could occur.
RIVER STATEMENT
Used to provide information about significant with-in river rises or for river stages nearing the listed flood stage. Also used to provide information about minor ice jams. They frequently contain river stage forecasts.
RIVER SUMMARY
Contains routine hydrological information. Also used to provide a summary of ongoing flooding events.
FLOOD POTENTIAL OUTLOOK
A late winter product used to provide information about expected hydrological conditions during the spring thaw.
FLASH FLOOD WATCH
Indicates that flash flooding is a possibility in or close to the watch area. Those in the affected area are urged to be ready to take action if a flash flood warning is issued or flooding is observed. These watches are issued for flooding that is expected to occur within 6 hours after the heavy rains have ended.
FLOOD WATCH
Indicates that widespread flooding is a possibility in or close to the watch area. Those in the affected area are urged to be ready to take action if a flood warning is issued or flooding is observed. These watches are issued for flooding that is expected to occur 6 to 12 hours after the heavy rains have ended.
FLASH FLOOD WARNING
A flood warning issued for life/property threatening flooding that will occur within 6 hours. It could be issued for rural or urban areas as well as for areas along the major rivers. Very heavy rain in a short period of time can lead to flash flooding, depending on local terrain, ground cover, degree of urbanization, amount of man-made changes to the natural river banks, and initial ground or river condition. Dam breaks or ice jams can also create flash flooding.
FLOOD WARNING (RIVER)
Used to inform the public of long-term (more than 12 hours) flooding along major streams and rivers, which is a serious threat to life or property. Usually contains river stage forecasts.
FLOOD WARNING
A flood warning issued for life/property threatening flooding that will occur 6 to 12 hours from time of issuance for widespread areas. It could be issued for rural or urban areas as well as for areas along the major rivers.

GREAT LAKES MARINE TERMS

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Following are various marine related terms related to severe weather or unusual water, waves, or wind conditions on the five Great Lakes.

DIGITAL MARINE WEATHER DISSEMINATION SYSTEM (D-MAWDS)
A menu-driven computer system which provides cooperating mariners with weather information such as observations, forecasts, charts, advisories, warnings, etc.
GALE WARNING
Issued when sustained winds will be 34 to 47 knots. These are wind speeds expected at end of downwind FETCH (nearshore or open waters).
GREAT LAKES FREEZE- UP OUTLOOK
This outlook, is issued by the Cleveland, Ohio NWS Forecast Office in the fall around November 1. It gives mariners information on whether ice conditions will occur earlier, later, or about the normal times over the Great Lakes. Selected water temperatures are included in this outlook.
GREAT LAKES STORM OUTLOOK & SUMMARY
The outlook gives mariners information on potential major large-scale storm development on the Great Lakes beyond the time period of routine 48 hour marine forecasts. The summary outlines the current status of a major large-scale storm system affecting one or more of the Great Lakes, and includes forecast information on the system's future effects.
LAKESHORE WARNING
A warning of potential or observed lakeshore flooding, or of high waves causing battering, or of an erosion situation, of ice jamming, or a seiche.
LAKESHORE STATEMENT
Used to give users advance notification of possible lakeshore warning situations, or to provide follow up information on shoreline warnings.
LAKES WEATHER BROADCAST (LAWEB)
An observation summary product prepared to provide mariners with a listing of all weather observations along or on the Great Lakes.
MARINE WEATHER STATEMENT
A statement issued to highlight single thunderstorms or lines of storms that are capable of producing wind gusts less than 34 knots, small hail, heavy rains, and dangerous lightning. Waves and winds are usually higher near a thunderstorm. This statement is also used to describe low-water conditions (which hampers boating traffic in shallow areas) at one end of a Great Lake (usually western Lake Erie) when sustained strong winds over a period of time pile up the water at the other side (downwind) of the lake. For low-water situations the "marine weather statement" is called a "Lakeshore Statement."
SPECIAL MARINE WARNING
Issued for weather conditions, usually of short duration (2 hours or less), producing sustained winds or frequent gusts of 34 knots or more. Large hail, very heavy rains, and dangerous lightning may occur. Waves and winds are usually higher near the thunderstorms. A Special Marine Warning will be issued for cold air funnels or waterspouts over the waters.
SMALL CRAFT ADVISORY
Issued for situations when winds are 18 to 33 knots or waves 4 feet or higher. Wind speeds and wave heights are those expected at end of FETCH (downwind portion of a forecast area; in this case the nearshore area).
STORM WARNING
Issued when sustained winds will be 48 knots or higher, either predicted or ongoing.

SAFFIR/SIMPSON HURRICANE SCALE


A scale ranging from one to five based on a hurricane's present intensity. This can be used to give an estimate of the potential property damage and flooding expected. In practice, wind speed is the parameter that determines the category since storm surge is highly dependent on the slope of the continental shelf.

Scale

Wind Speed (mph)

Storm Surge (ft)

Damage

1 74-95 4-5 Minor
2 96-110 6-8 Moderate
3 111-130 9-12 Major
4 131-155 13-18 Severe
5 Greater than 155 Greater than 18 Catastrophic

COASTAL/OCEANIC MARINE TERMS

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Following are various marine related terms related to severe weather or unusual water, waves, current, or wind conditions over the coastal waters and open Atlantic and Pacific Oceans.

ADVISORY
Official information issued by Tropical Cyclone Centers, such as the National Hurricane Center near Miami FL. Describes all tropical cyclone watches and warnings in effect along with details concerning locations, intensity, movement and precautions that should be taken. Advisories are also issued to describe tropical cyclones prior to issuance of watches and warnings and subtropical cyclones.
COASTAL FLOOD STATEMENT
Keeps the public and cooperating agencies informed of the status of existing coastal flood watches and warnings, as well as provides an update on local conditions. Also used to cancel a watch or warning.
COASTAL FLOOD WATCH/WARNING
A coastal flood watch alerts coastal residents to the possibility of flooding. A coastal flood warning means that flooding is imminent or occurring. Coastal waters extend out 100 nautical miles.
GALE WARNING
Warns the public that sustained winds of 34 to 47 knots (39 to 54 mph) inclusive are expected or occurring and are not directly associated with tropical cyclones.
HEAVY SURF ADVISORY
Advises people that heavy (high) surf that may pose a threat to life or property. Such advisories may be issued alone or in conjunction with coastal flood watches or warnings.
HURRICANE EYE
The relatively calm area in the center of the storm. In this area, winds are light and the sky often is only partly covered by clouds.
HURRICANE SEASON
The part of the year having a relatively high incidence of hurricanes. In the Atlantic, Caribbean, Gulf of Mexico and central Pacific, the hurricane season is the period from June through November.
HURRICANE LOCAL STATEMENT
A public release in or near the threatened area giving specific details on (1) weather conditions, (2) evacuation decisions made by local officials, and (3) other necessary precautions to protect life and property.
HURRICANE WATCH
An announcement for specific areas that a hurricane poses a possible threat to coastal areas generally within 36 hours.
HURRICANE WARNING
A warning that sustained surface winds of 64 knots (74 mph) or higher are expected in specified coastal areas within 24 hours or less. A hurricane warning can remain in effect when dangerously high water and/or exceptionally high waves continue even though winds may be less than hurricane force.
INLAND HIGH WIND WATCHES FOR HURRICANE FORCE WINDS
Issued for inland locations when hurricane force winds or greater winds are anticipated beyond the coastal areas though the actual occurrence, timing and location are still uncertain.
PROBABILITY OF TROPICAL CYCLONE CONDITIONS
The probability, in percent, that the cyclone center will pass within 50 miles to the right or 75 miles to the left of the listed locations within the indicated time period when looking at the coast in the direction of the cyclone's movement.
SPECIAL TROPICAL DISTURBANCE STATEMENT
Issued to furnish information on strong formative, nondepression systems. It focuses on major threats of the disturbance, such as the potential for torrential rains on island or inland areas.
STORM SUMMARY
Issued by the National Hurricane Center after subtropical and tropical cyclones have moved inland and advisories have been discontinued. These summaries are initiated when and if flash flood watches are posted in the conterminous U.S. because of an approaching system.
STORM SURGE
An abnormal rise in sea level accompanying a tropical cyclone. The height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the storm. Storm surge is usually estimated by subtracting the normal or astronomical tide from the observed storm tide.
STORM TIDE
The actual sea level resulting from the astronomical tide combined with the storm surge. This term is used interchangeably with "hurricane tide".
STORM WARNING
A warning that sustained winds of 48 knots (55 mph) or greater are expected or occurring and are not directly associated with tropical cyclones.
STRIKE PROBABILITY FORECAST OF TROPICAL CYCLONE CONDITIONS
A product issued to describe the probability of tropical cyclone conditions to affect a given area within a range of time periods. It is issued for named storms.
TROPICAL CYCLONE DISCUSSION
Issued to explain the forecaster's reasoning behind the analysis and forecast of tropical cyclone characteristics.
TROPICAL CYCLONE POSITION ESTIMATE
Issued to give a position estimate between 2-hourly intermediate advisories whenever the storm center is within 200 nautical miles of U.S. land-based radar to allow for a reliable radar center fix.
TROPICAL CYCLONE PUBLIC ADVISORIES
Serve as the primary tropical cyclone information products issued by Tropical Cyclone Centers for the general public. They are issued after a confirmed tropical cyclone has developed. Sub-group product names in this category are: Special Public Advisory, Intermediate Public Advisory, Tropical Depression Advisory, Subtropical Cyclone Public Advisory, and Special Public Subtropical Forecast/Advisory.
TROPICAL CYCLONE PUBLIC ADVISORIES
Serve as the primary tropical cyclone information products issued by Tropical Cyclone Centers for the general public. They are issued after a confirmed tropical cyclone has developed. Sub-group product names in this category are: Special Public Advisories, Intermediate Public Advisories, and Tropical Depression Advisory.
TROPICAL CYCLONE UPDATES
Brief statements issued in lieu of or preceding special advisories to inform of significant changes in a tropical cyclone, or to post or cancel watches and warnings.
TROPICAL STORM WATCH
An announcement that a tropical storm or tropical storm conditions pose a threat to coastal areas generally within 36 hours. A tropical storm watch is not usually issued if a tropical cyclone is forecast to attain hurricane strength.
TROPICAL STORM WARNING
A warning that sustained winds of 34 to 63 knots (39 to 73 mph) inclusive are expected in specified coastal areas within 24 hours or less.
TROPICAL WEATHER DISCUSSION & OUTLOOK & SUMMARY
The discussion describes significant synoptic (large-scale) weather features in the tropics. The outlook discusses significant areas of disturbed weather in the tropics and subtropics and their potential for tropical cyclone development out to 48 hours. The summary is prepared after each month to summarize the previous month's tropical cyclone activity or lack of activity and the reasons why.

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