tidetable

Tidetable is a Python module for downloading annual tide prediction tables from the NOAA Tides & Currents site.

Install with pip install tidetable.

Basics

First, get the Station ID for your tide station from the NOAA Tides & Currents site.

Then, use the get method to download the table. This returns a TideTable object, which is just a list with a few additional metadata parameters.

In this example, we use a tide station in Maine:

>>> import tidetable
>>> table = tidetable.get(8416092, datum='MLLW')
>>> table
tidetable.TideTable(stationid=8416092)
>>> table[0]
{'pred_cm': 149.0, 'datetime': datetime.datetime(2014, 12, 31, 3, 44), 'pred_ft': 4.9, 'high_low': 'H'}

The TideTable object's metadata includes some location data, information about the parent tide station, and error intervals:

>>> table.stationname, table.state
('Monhegan Island', 'ME')
>>> table.datum
'MLLW'
>>> table.referencetostationid
'8418150'
>>> table.timeoffsetlow, table.timeoffsethigh
('-9', '-13')

Time frames

By default, the NOAA returns the tide prediction table for the current year. To get years in the recent past or future, use the year keyword argument. It seems that roughly five years in the past and two years in the future are available. There isn't a way to get smaller time ranges of predictions than a full year.

>>> import tidetable
>>> table = tidetable.get(8416092, year=2019, datum='MLLW')
>>> table
tidetable.TideTable(stationid=8416092)
>>> table[4]['datetime']
datetime.datetime(2016, 1, 1, 3, 39)

(Note that the first few rows returned may be for the previous year.)

Writing

The TideTable object has a write_csv method. It accepts either a file name or any file-like object.

import tidetable
table = tidetable.get(8416092, datum='MLLW')
table.write_csv('tide_table.csv')

Command line tool

Tidetable has a simple command line interface, which can be used when running the module as a script:

$ python -m tidetable --help
usage: tidetable [-h] [--year YEAR] [--datum {STND,MHHW,MHW,MTL,MSL,MLW,MLLW}]
                 station-id

positional arguments:
  station-id            NOAA station id

optional arguments:
  -h, --help            show this help message and exit
  --year YEAR           year
  --datum {STND,MHHW,MHW,MTL,MSL,MLW,MLLW}
                        output datum

Time zones

As you can see, TideTable is a list of dicts, each of which has a datetime, a prediction in feet and cm, and a high-or-low flag. The predictions are relative to the datum, which in this case is MLLW, or the mean lower low water level. Note that MLLW is different from sea level.

By default, the datetime is in the local time, which could be standard or daylight savings time. Use the time_zone keyword argument to fetch times in either GMT or the local standard time zone. TideTable always returns naive datetime objects.

Use these constants for specifying the time zone: tidetable.GMT, tidetable.LOCAL_STANDARD_TIME, tidetable.LOCAL_TIME.

>>> import tidetable
>>> table = tidetable.get(8416092, time_zone=tidetable.GMT)
>>> table[0]['datetime']
datetime.datetime(2014, 12, 31, 0, 15)

(Note the difference from the datetime in the first example, which is in Eastern Standard Time)

fitnr / tidetable