## Lunitidal interval Definition

It is the mean time interval between the transit of the moon over the local meridian and the next high or low tide. Tides are periodic rises as well as falls of ocean water that are caused by the gravitational interaction between the Earth and the Moon.

It generally gives the time difference between two natural events that occurs simultaneously. The first event is when the moon passes over a meridian. The second event happens when the corresponding water tide reaches its highest peak. Practically, these two events do not take place simultaneously due to certain geographical features and disturbances. This in turn causes a time lag or interval between the transit of the moon and when the tide attains the highest level. It is also known as high water interval (HWI).

## Lunitidal interval Factors

A strong peak in the tidal forces can be observed when the moon is at the meridian for a given location. However, there is always a delay before the occurrence of a high tide that typically varies from place to place. According to the lunar phase, the lunitidal interval fluctuates within about +/- 30 minutesEn stock. Some of the factors that normally cause this delay include:

- Inertia
- Friction
- Shape of the coastline
- Sea floor/water depth

## Lunitidal interval Calculator

Calculation of the lunitidal interval will give an accurate prediction during a high tide. In order to get an approximate value, the moon-rise, moon-set and high tide times should be known for a specific location.

To determine the moon-rise and moon-set, one must use the following steps:

- Go to http://www.timeanddate.com/worldclock/moonrise.html
- Select your location and then click on “See moonrise/moonset”
- The resulting table gives the lists of moonrise/moonset times for the coming seven days. To view the list of moonrise/moonset times for the whole month, click on the “Modify Parameters” box at the top of the table. Then click on the “Show” tab. The same box can be utilized to select a different month or year from the previous one.
- Once you have seen your desired date in the table generated in the earlier step, look at the “Time” column under “Merdian Passing”, which is just to the right of the “Moonset” column. The time listed in correspondence to the date is when the moon passes over the meridian on that particular date. Note down this time, along with the date.
- The meridian time that was written in the previous step must be converted from AM/PM to 24-hour time. For your convenience the link, which is given below can do the conversion in case of any difficulty. Carefully, note down this new time, along with the date.

In order to determine the high tide time one must adhere to the following steps:

- Go to http://tbone.biol.sc.edu/tide/sites_allalpha.html
- A list of sites is displayed from which you can select your desired location
- The resulting table gives the tidal information for the next two days. Scroll down to “Prediction Options” if you want information for a different date and reset the fields under the tab “Starting time and time display options” for the required date. Again scroll down to the bottom of the page and click “Make Prediction Using Options”.
- Once you have generated a table, listing your desired date find the first high tide occurring after the 24-hour meridian time you noted down previously. Note down the high tide time, along with the date.

The steps that need to be followed in order to calculate the lunitidal interval are:

- Go to http://www.onlineconversion.com/days_between_advanced.htm
- Enter the previous value of the 24-hour meridian date and time in the “First date and time” field.
- Similarly in the “Second date and time” field, enter the high tide date and time that you noted down earlier.
- Click on the “Calculate” tab
- The resulting time will give you the lunitidal interval.

## Lunitidal interval UK

There are some clocks and watches such as tide clocks that generally work by using a 12 hour 25 minutes cycle. In the UK and Ireland, these devices would vary between plus or minus 30 minutes over a span of 30 days. Hence, it is essential to reset them on a monthly basis by using local tide tables. Tide or tidal watches have a moon/tide mode that require lunitidal intervals in order to predict high and low tide.

Mean lunitidal intervals can be calculated using the following formula:

Interval (hrs) = M2 phase (degrees) x M2 period (hrs) / 360 (degrees)

The table below can be used to set the moon/tide mode of the watch:

Port/Location |
Latitude |
Longtiude |
Interval(hrs : mins) |

ST. HELIER | 49° 11’N | 2° 7’W | 6:18 |

ST. MARY’S | 49° 55’N | 6° 19’W | 4:31 |

NEWLYN | 50° 6’N | 5° 33’W | 4:36 |

FALMOUTH | 50° 9’N | 5° 3’W | 5:02 |

PLYMOUTH (DEVONPORT) | 50° 22’N | 4° 11’W | 5:18 |

NEWQUAY | 50° 25’N | 5° 5’W | 4:53 |

TORQUAY | 50° 28’N | 3° 31’W | 5:51 |

PORTLAND | 50° 34’N | 2° 26’W | 6:40 |

WEYMOUTH | 50° 36’N | 2° 27’W | 6:36 |

BOURNEMOUTH | 50° 43’N | 1° 52’W | 9:24 |

CHRISTCHURCH (QUAY) | 50° 44’N | 1° 46’W | 10:37 |

LYMINGTON ENTRANCE | 50° 44’N | 1° 30’W | 11:02 |

ISLE OF WIGHT – COWES | 50° 46’N | 1° 18’W | 11:21 |

NEWHAVEN | 50° 47’N | 0° 3’E | 11:05 |

PORTSMOUTH | 50° 48’N | 1° 7’W | 11:16 |

LITTLEHAMPTON | 50° 48’N | 0° 32’W | 11:08 |

SHOREHAM | 50° 50’N | 0° 15’W | 11:06 |

DUNGENESS | 50° 54’N | 0° 58’E | 11:14 |

SOUTHAMPTON | 50° 54’N | 1° 24’W | 11:19 |

DOVER | 51° 7’N | 1° 19’E | 11:27 |

ILFRACOMBE | 51° 13’N | 4° 7’W | 5:36 |

HINKLEY POINT | 51° 13’N | 3° 8’W | 6:19 |

MINEHEAD | 51° 13’N | 3° 28’W | 6:11 |

MARGATE | 51° 24’N | 1° 23’E | 11:47 |

SHEERNESS | 51° 27’N | 0° 45’E | 12:12 |

TILBURY | 51° 27’N | 0° 22’E | 0:18 |

NORTH WOOLWICH | 51° 30’N | 0° 5’E | 0:44 |

SHIVERING SANDS | 51° 30’N | 1° 5’E | 11:59 |

LONDON BRIDGE | 51° 30’N | 0° 5’W | 1:10 |

AVONMOUTH | 51° 31’N | 2° 43’W | 6:57 |

SOUTHEND | 51° 31’N | 0° 43’E | 12:11 |

CORYTON | 51° 32’N | 0° 31’E | 12:24 |

NEWPORT | 51° 33’N | 2° 59’W | 6:44 |

MUMBLES | 51° 34’N | 3° 59’W | 5:57 |

SWANSEA | 51° 37’N | 3° 55’W | 5:57 |

MILFORD HAVEN | 51° 42’N | 5° 3’W | 5:58 |

RINGASKIDDY | 51° 50’N | 8° 19’W | 5:15 |

COBH | 51° 50’N | 8° 18’W | 5:09 |

WALTON-ON-THE-NAZE | 51° 51’N | 1° 16’E | 11:25 |

CORK CITY | 51° 54’N | 8° 27’W | 4:15 |

HARWICH | 51° 57’N | 1° 17’E | 11:18 |

MISTLEY QUAY | 51° 57’N | 1° 5’E | 11:30 |

FELIXSTOWE | 51° 57’N | 1° 21’E | 11:05 |

FISHGUARD | 52° 1’N | 4° 59’W | 7:09 |

ROSSLARE HARBOUR | 52° 15’N | 6° 21’W | 5:25 |

BARROW BRIDGE | 52° 16’N | 7° 0’W | 5:25 |

ABERYSTWYTH | 52° 25’N | 4° 6’W | 7:55 |

LOWESTOFT | 52° 28’N | 1° 45’E | 8:57 |

GORLESTON | 52° 34’N | 1° 44’E | 8:17 |

RIVER SHANNON TARBERT ISLAND | 52° 35’N | 9° 22’W | 5:17 |

BARMOUTH | 52° 43’N | 4° 3’W | 8:14 |

KING’S LYNN | 52° 45’N | 0° 24’E | 6:34 |

WEST LIGHTHOUSE | 52° 49’N | 0° 13’E | 6:17 |

WEST STONES | 52° 49’N | 0° 21’E | 6:19 |

ROARING MIDDLE (WASH) | 52° 55’N | 0° 18’E | 6:04 |

TABS HEAD | 52° 56’N | 0° 5’E | 6:13 |

HUNSTANTON | 52° 56’N | 0° 29’E | 6:11 |

CROMER | 52° 56’N | 1° 18’E | 6:29 |

GIBRALTAR POINT | 53° 5’N | 0° 20’E | 5:54 |

SKEGNESS | 53° 9’N | 0° 21’E | 5:47 |

GALWAY | 53° 16’N | 9° 3’W | 4:50 |

BOYGRIFT | 53° 18’N | 0° 18’E | 5:38 |

EASTHAM | 53° 19’N | 2° 57’W | 11:22 |

HOLYHEAD | 53° 19’N | 4° 37’W | 10:04 |

INNER DOWSING (WASH) | 53° 19’N | 0° 35’E | 5:35 |

LLANDUDNO | 53° 20’N | 3° 49’W | 10:41 |

DUBLIN (NORTH WALL) | 53° 21’N | 6° 13’W | 11:16 |

HILBRE ISLAND | 53° 23’N | 3° 13’W | 10:57 |

BIRKENHEAD (ALFRED LOCK) | 53° 24’N | 3° 1’W | 11:09 |

LIVERPOOL (PRINCES PIER) | 53° 25’N | 3° 0’W | 11:09 |

LIVERPOOL (GLADSTONE LOCK) | 53° 27’N | 3° 1’W | 11:04 |

BULL SAND FORT | 53° 33’N | 0° 4’E | 5:16 |

SPURN POINT | 53° 35’N | 0° 7’E | 5:12 |

IMMINGHAM | 53° 38’N | 0° 11’W | 5:35 |

BLACKTOFT | 53° 41’N | 0° 42’W | 6:58 |

HULL | 53° 44’N | 0° 21’W | 5:59 |

WITHERNSEA | 53° 44’N | 0° 2’E | 4:37 |

FLEETWOOD | 53° 55’N | 3° 0’W | 11:15 |

HEYSHAM | 54° 2’N | 2° 55’W | 11:14 |

HALFWAY SHOALS | 54° 2’N | 3° 12’W | 11:11 |

ROA ISLAND | 54° 4’N | 3° 10’W | 11:20 |

PORT ERIN | 54° 5’N | 4° 46’W | 11:05 |

BARROW (RAMSDEN DOCK) | 54° 6’N | 3° 13’W | 11:24 |

DOUGLAS | 54° 9’N | 4° 28’W | 11:16 |

SCARBOROUGH | 54° 17’N | 0° 23’W | 3:49 |

WHITBY | 54° 29’N | 0° 37’W | 3:35 |

BELFAST | 54° 36’N | 5° 55’W | 10:54 |

RIVER TEES ENTRANCE | 54° 38’N | 1° 9’W | 3:18 |

WORKINGTON | 54° 39’N | 3° 34’W | 11:27 |

BANGOR (N.IRELAND) | 54° 40’N | 5° 40’W | 10:57 |

PORTPATRICK | 54° 51’N | 5° 7’W | 11:27 |

LARNE | 54° 51’N | 5° 47’W | 10:55 |

RIVER TYNE (NORTH SHIELDS) | 55° 0’N | 1° 26’W | 3:04 |

LONDONDERRY | 55° 0’N | 7° 19’W | 8:10 |

COLERAINE | 55° 10’N | 6° 46’W | 6:50 |

PORTRUSH | 55° 12’N | 6° 40’W | 6:47 |

MALIN HEAD | 55° 18’N | 7° 15’W | 6:07 |

ISLAY (PORT ELLEN) | 55° 38’N | 6° 11’W | 3:07 |

MILLPORT | 55° 45’N | 4° 54’W | 11:49 |

GREENOCK | 55° 58’N | 4° 49’W | 11:55 |

LEITH | 55° 59’N | 3° 11’W | 1:54 |

ROSYTH | 56° 1’N | 3° 27’W | 1:53 |

OBAN | 56° 25’N | 5° 29’W | 5:38 |

TOBERMORY | 56° 37’N | 6° 4’W | 5:49 |

ABERDEEN | 57° 9’N | 2° 4’W | 0:50 |

MORAY FIRTH | 57° 36’N | 4° 0’W | 11:37 |

CROMARTY FIRTH | 57° 41’N | 4° 1’W | 11:33 |

ULLAPOOL | 57° 54’N | 5° 9’W | 6:55 |

STORNOWAY | 58° 12’N | 6° 23’W | 6:49 |

WICK | 58° 26’N | 3° 5’W | 11:07 |

KINLOCHBERVIE | 58° 27’N | 5° 3’W | 7:10 |

LERWICK | 60° 9’N | 1° 8’W | 10:45 |

SULLOM VOE | 60° 27’N | 1° 18’W | 9:13 |

## Lunitidal interval Chart

**References:**

http://www.cyberspaceconstructor.com/Lunitidal_Interval_Data_List.php

http://www.ehow.com/how_5269223_calculate-lunitidal.html

http://www.pol.ac.uk/ntslf/sharing_knowledge.php

http://www.hydro.gov.au/prodserv/tides/lunitidal-intervals.htm

http://pathfinder.casio.com/support/