WHAT’S A MAREP? In summary, MAREPs are valuable be-cause...YOU KNOW THE WEATHER!
MAREP stands for MAriner REPort. AMAREP is a radio message of weatherand sea conditions observed by you andother mariners at sea.
WHY SEND MAREPs?
Because you’re at sea and you know theweather. Timely weather observations -MAREPs - taken and transmitted by youare important. Here’s why:
l Your observations help theNational Weather Service(NWS) improve the accuracyand timeliness of marineweather warnings and forecasts.
l Your observations fill in thespaces between widelyseparated weather reportingships and buoys. This helps toidentify weather conditions thatmight otherwise go undetected.
l NWS warnings and forecasts,which are updated from marineobservations, are quicklyrelayed via telecommunicationscircuits and over radio toboaters, fishermen, and otherswho depend on weatherinformation for work and leisureat sea.
SO...WHAT’S IN IT FOR ME?
MAREPs mean self-help. By sending aMAREP you benefit from better warningsand forecasts.
GUIDELINES
I. Call the radio station and tell them youwant to transmit a MAREP.
2. Report as much as you can. Even par-tial reports are important.
3. Try to send a MAREP at least onceduring the operating hours of the radiostation, or more often if possible. Also,send a MAREP when the weather chan-ges or is different than the forecast.
4. Report information in the same orderas presented in this manual. Since othermariners are reporting the same way, itwill be easier and faster for the radiooperator to relay the MAREPs to the NWS.
HOW TO DO IT
A complete MAREP contains the follow-ing information:
WhoWhenWhere
1. Your call sign or vessel name2. Time of observation3. Approximate location where
observation was made
Very important. 4. Wind direction and speedWhat you and 5. Seasthe forecasters 6. Swellneed to know. 7. Visibility
8. Present WeatherOptional. If you 9. Barometer (Air Pressure)can, try to report 10. Air temperaturethese too. 11. Sea Temperature
Feel free! 12. Remarks
HERE ARE THE DETAILS
1. YOUR CALL SlGN;l dentify yourself bythe radio call sign or name of your vessel.
Example: “THIS IS WXY-123” or “THIS ISTHE NINA J.”
2. TIME OF 0BSERVATlON:Give thetime that you took the weather observa-tion, not the time you called in the report.Use local time. Try to use the 24 hourclock (add 12 to PM times).
Time of observation is very important be-cause your MAREP can be compared toobservations taken at other locations atabout the same time.
E OBSERVATION:Give location either as
latitude and longitude to the nearest tenthof a degree or an approximate distanceand d i rect ion f rom a wel l -knownlandmark. Report location when observa-tion was taken, not when it was called in.
Example: 35.3 74.7 or 60 MILES EASTOF HATTERAS LIGHT
4. WIND DlRECTlON:The direction thewind is blowing from. Report one of the 8points of the compass:
N, W, S, W, NE, SE, SW, or NW.
Direction can be estimated by observingthe movement of waves produced bywinds in the local area. However, do notuse the direction of swell (see item 6) orthe movement of clouds to estimate sur-face wind direction.
If you have a reliable, calibrated aerovaneon board, average the directions overabout a 1 minute period and report theaverage direction from the list above.
WIND SPFFDLReported in knots (nauti-cal miles per hour). Estimate the windspeed to nearest 5 knots. If there’s little orno wind, report calm.
If you have a rel iable, cal ibratedanemometer on board, average thespeeds over about a I minute period andreport the average to the nearest knot.
WIND GUSTS:Rapid fluctuations in windspeed with a variation of 10 knots or morebetween peaks and lulls. Report inRemarks (item 12 below) the estimatedgust speed or the word GUSTY.
Examples of wind reports:
NW 20 ..GUSTY (IN REMARKS)SE15W 25...GUSTS TO 40 (in REMARKS)CALM
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NOTE: The above instructions will assistyou in coming up with a good estimate ofwind conditions. A group of estimatedreports from mariners in the area givesthe forecaster a better picture of what’sgoing on than he had before. And thatmeans more confidence in whether or notto issue a warning. If you are estimatingwind direction and speed aboard a.moving vessel by methods othe than ob- :
serving the appearance of the sea {Ap-pendix I), see Appendix 2 which showsyou how to use the slide rule calculatorfound in the pocket of this manual,
5. SEAiWaves produced by winds in thearea. Wind-driven waves have a mixedappearance with many different heightsand distances between waves. Waveheight is the vertical distance from trough(low point of wave) to crest (high point ofwave). Report the average m height to the
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nearest foot of yvell-formed wavesproduced by winds in the area. Avoidtaking a “snapshot” observation. Try toobserve the sea for a couple of minutesto arrive at the average - or what theforecaster refers to as the “significant”height.
If an unusually high wave, much higherthan average, occurs every now and thenduring your observation, give its height inRemarks (item 12 below).
Example: SEAS 8 FEET (average of ob-served heights)....HlGHEST WAVE 15FEET (in Remarks)
6 SWELWaves that are present, butnot produced by winds in the area. Thesewaves are more regular and uniform inappearance and have a longer wave
length (crest-to-crest distance) andlonger period (time between passage ofwave crests). Swell are waves that havecome from a distant storm. It’s possibleto experience high swell even when thewind is light or calm.
tiox Report the direction the swellis coming from.
H&&Q& Average height to the nearestfoot from trough to crest.
7. VlSlBlLlTY;The greatest distance thata known object can be seen and iden-tified. When there are no objects to iden-tify (as is so often the case in the middleof the ocean), visibility can be obtained byestimating the distance to the horizon ac-cording to the following table:
Distance To Horizon At Sea (Nautical Miles
Height ofObservation Distance to
Height ofObservation Distance to
Platform (Ft.) Horizon (n. mi.) Platform (Ft.) Horizon (n, mi.)
5 3 25-30 610-15 4 35-40 7
20 5
If the object or horizon is visible with littleor no blurring, visibility is greater than thedistance. If object or horizon is blurred orindistinct, visibility is about equal to thedistance.
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Report the average distance in miles youcan see in the area around your vessel.For less than 1 mile, report to nearestquarter mile. If visibility varies widelyaround the area, report the average dis-tance and give the minimum distance inRemarks (item 12 below). You need notreport a minimum distance unless it is 1mile or less.
Example: Visibility varies from 1/4 mile to3 miles around your vessel, but averages2 miles over most of the area. ReportVISIBILITY 2 MILES. At the end of yourreport in REMARKS give the minimumvisibility such as: VISIBILITY I/4 MILE INPATCHY FOG
8. PRESENT WEATHERLRefers toclouds, precipitation, and obstructions tovision. Report the weather that bestdescribes local conditions at the time ofobservation. Up to three of the followingconditions may be reported. (ReportCloudy, Partly Cloudy, or Clear only whenthere is no precipitation.)Clear Drizzle SnowPartly Cloudy Freezing Drizzle HailCloudy bin ThunderstormFog Freezing Rain SquallHaze Sleet Waterspout
You know the weather, but just in case...
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Clear: 0 to 2/10 of the skycovered.Partly Cloudy: 3/10 to 7/10 ofthe sky covered.Cloudy: 8/10 to lo/IO of the skycovered.
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Fog: Tiny water dropletssuspended in the air withoutvisible downward motion andhaving a gray color.Haze: Tiny dust or salt particles
suspended in the air. Haze isusually distinguished from fogby its blueish or yellowish color.Drizzle: Very small waterdroplets that appear to float inair currents, but fall to thesurface.Freezing Drizzle: Drizzle thatfreezes on contact withexposed surfaces that arebelow freezing.Rain: Liquid water drops.
Freezing Rain: Rain that freezeson contact with exposedsurfaces that are below freezing.Sleet: Frozen rain.
Snow: Ice crystals often in theshape of six-sided flakes.Hail: Ice balls, equal or greaterin size than raindrops. Usuallyassociated with a thunderstorm.
Thunderstorm: Thunder mustbe heard. Lightning may ormay not be seen.Thunderstorms may occurwithout precipitation.
Squall: A sudden increase inwind and an abrupt lowering ofclouds with or withoutprecipitation or heavy seaconditions.Waterspout: Sometimesreferred to as a tornado overwater. A rotating column of airand spray with very high windsand a loud roaring noise.Funnel-shaped appendagetouching the water, suspendedfrom the base of clouds.
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P’ ,
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.The following parts of a MAREP’.are notas important ‘as the.elements describedso,far. But if:you have the instrumentation‘.(reliable, of course), try to include.them inyour .MAREP::: ..:.:..
9. BAROMETER [Air PressurelJf youhave a barometer that’s been calibratedrecently, tap the dial lens and read the airpressure. Be sure to view the pointer headon. Some barometers have a mirror stripnext to the dial markings. The reflection ofthe pointer should be lined up right behindthe pointer itself. Read the dial to thenearest hundredth of an inch or nearestwhole millibar (depending on type ofbarometer).
10. AIR TEMPERATURl2Report to thenearest whole degree fahrenheit.
I I. SEA TEMPERATURE:Report to thenearest whole degree fahrenheit.
Last but definitely not least:
12. REMARKS:Here’s your chance tosay anything you want, within reason, ofcourse. Report any additional data orconditions that you believe the forecasterneeds to know. Additional data includewind gusts (see item 4) wave heightsmuch higher than average (see item 5)and minimum visibility (see item 7). Hereare some examples.
DARK CLOUDS NWHEAW FtAlNGUSTS TO 40 KNOTSSEAS TO 30 FEETLIGHTNING NW
WIND LIGHT AND VARIABLEVISIBILITY 1/4 Ml IN PATCHY FOGWAVES LIKE GFtAND CANYONFREEZING SPRAYWHO MADE THAT FORECAST?. ..ETC...
MAREP EXAMPLE
Here’s what a MAREP relayed to NWSwould look like with all the elementsreported. But, please remember, evenif you send a partial report, such asonly winds and seas, your MAREP isimportant.
Inside the pocket of this manual is aMAREP guide which summarizes the in-structions. Use it as a handy reference intaking and sending an observation.Before long, it’ll be like second na-ture....And that’s just what we want...tohave you add MAREP reporting to yournavigational routine...to help the NationalWeather Service help you.
Your MAREPs are valuable, are ap-preciated, and they do make a differencebecause.. .
YOU KNOW THE WEATHER!
Thanks for your help...and tell othersto send MAREPs.
Figure 2.Wind speed 1-3 kt, average 2 kt
Sea Criterion: Ripples with the appearance of scales areformed, but without foam crests.
Waves at time of picture Height (ft) Period (sec)
Sea wavesSwell 3 10
Height of camera above sea: 35 ft.
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1
Figure 4.Wind speed 7-10 kt, average 9 kt
Sea Criterion: Large wavelets. Crests begin to break. Foamof a glassy appearance. Perhaps scatteredwhite horses.
Waves at time of picture Height (ft) Period (set)
Sea wavesSwell a 7
Height of camera above sea: 45 ft.
A
IO
Figure 5.
Wind speed 11-16 kt, average 13 kt
Sea Criterion: Small waves, becoming longer, fairly frequentwhite horses.
Waves at time of pictureSea wavesSwell
Height (ft)3
Period (set)5
Height of camera above sea: 35 ft.
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Figure 6.Wind speed 17-21 kt, average 19 kt
Sea Criterion: Moderate waves taking a more pronounced longform; many white horses are formed. (Chance ofsome spray.)
Waves at time of picture Height (ft) Period (set)Sea waves 7 6Swell 6 8
Height of camera above sea: 35 ft.
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Figure 7.Wind speed 22-27 kt, average 24 kt
Sea Criterion: kge waves begin to form; the white foam crestsare more extensive everywhere. (Probably some spray)
Waves at time of picture Height (ft) Period (set)Sea waves 11 6Swell -
Height of camera above sea: 20 ft.
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Figure 8.Wind speed 28-33 kt, average 30 kt
Sea Criterion: Sea heaps up and white foam from breaking wavesbegin to be blown in streaks along the direction ofthe wind.
Waves at time of picture Height (ft) Period (set)
Sea waves 13 6Swell 10 9
Height of camera above sea: 45 ft.
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Figure 9.Wind speed 34-40 kt, average 37 kt
Sea Criterion: Moderately high waves of greater length; edges ofcrests begin to break into the spindrift. The foam isblown in well-marked streaks along the directionof the wind.
Waves at time of pictureSea waves
Height. (ft)18
Period (set)7
SwellHeight of camera above sea: 35 fi.
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F
Figure 10.Wind speed 41-47 kt, average 44 kt
Sea Criterion: High waves. Dense streaks of foam along thedirection of the wind. Crests of waves begin totopple, tumble, and roll over. Spray may affectvisibility.
Waves at time of picture
Sea wavesSwell
Height (ft)
20
Period (set)
7
Height of camera above sea: 35 ft.
Figure 11.Wind speed 48-55 kt, average 52 kt
Sea Criterion: Very high waves with long overhanging crests.The resulting foam, in great patches, is blown indense white streaks along the direction of the wind.On the whole, the sutface of the sea takes on awhite appearance. The tumbling of the sea becomesheavy and shocklike. Visibility affected.
Waves at time of picture
Sea wavesSwell
Height (ft)
22
Period (set)9
Height of camera above sea: 15ft.
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Appendix 2
FIGURING TRUE WIND FROMAPPARENT WIND
Remember the old saying about “separat-ing the wheat from the chaff”? Well, it alsoapplies to taking wind observations on amoving vessel. In this case it’s a matterof separating the true wind from the ap-parent wind.
True wind is what the direction and speedwould be if your vessel were anchored.Apparent wind is the wind experienced ona moving vessel which is a combinationof true wind and vessel movement. Truewind direction is always on the same sideof the vessel as the apparent wind direc-tion, but farther from the bow.
Enclosed in the pocket of this manual is aslide rule calculator to convert apparentwind direction and speed (estimated ormeasured) to true wind direction andspeed based on the speed and headingof your vessel.
The instructions printed on the calculatorare self-explanatory. Basically, here’swhat it
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does:
After you determine theaparent wind direction andspeed off the bow, it tells youwhat the m wind direction andspeed would be off the bow ifthe ship were anchored.
Then, based on the ship’sheading, it converts the truewind direction off the bow to acompass direction which iswhat you would report in yourMAREP.
An example is given on the next page.
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Here’s an example situation for using thecalculator:
Say you’re heading 135 degrees (SE) at15 knots. Winds are picking up and youdecide to call in a MAREP. The wind feelslike it’s hitting you about 60 dearees offthe starboard bow. This is your AP-PARENT WIND DIRECTION. Now, look atthe scale on the calculator labled ,A&PARENT WIND SPEED. Pick a speedthat’s closest to what you think the windis blowing, say, 30 knots.
Just to make sure you know how to usethe calculator, try this exercise. In theabove example, what if the apparent windwas hitting you at 60 dea ees off the oort&? What would your Compass direc-tion be? If you say NE, you’re right. All theabove steps are the same except that instep 3 you turn the true wind arrow to 90degrees port on the “ship.” With the “ship”pointed to 135 degree heading the windarrow is pointing to the NE.
Summarv...
I. Move the sliding card and line up 60degrees (apparent wind direction) with 15knots (ship speed).
2. Look across the apparent wind speedscale. Above and below 30 knots readTRUE WIND DIRECTION of 90 degreesand TRUE WIND SPEED of 25 knots,repectively. Since the true wind directionis also off the starboard bow. it has to beconverted to a comoass direction
3. Turn the wind arrow to 90 degrees star-board on the scale printed on the “ship.”Holding the arrow steady, turn the “ship”to 135 degrees (ship heading) on theouter scale.
4. The wind arrow now points to the SWon the outer scale. So, your wind reportin your MAREP is SW 25 knots. (Thespeed is from step 2.)
I. Determine apparent wind direction(port or starboard), apparent wind speed,and ship heading and speed.
2. Align apparent wind direction with shipspeed.
3. Read off true wind direction (port orstarboard) and true wind speed.
4. Align wind arrow on ship scale (port orstarboard).
5. Align ship with heading,
6. Read off compass wind direction andreport it, together with true wind speed inyour MAREP.
