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Long Island Sound tidal current model ready for the Vineyard Race

Posted by Penny Haire on 3 September 2020 6:53:30 PM
Penny Haire


We are very excited to release our new model of Long Island Sound in time for the Vineyard Race this Friday. With a resolution of 110m the model covers the race area in incredible detail, showing for the first time how the tidal currents flow around key locations across the course.

A Navigator's Race

The Vineyard Race is truly a classic coastal race, similar in many ways to the famous Fastnet Race where strong and complex tidal currents and a mixture of wind conditions are a test for even the most experienced navigators. This year the tides will be especially important as the race will be just after the full moon - and so big, Spring Tides up to 4 kts in places.

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Key locations

Regular competitors will already know how vitally important the following locations are to the result:

  1. The Race (passage between Little Gull Island and Fishers Island)
  2. Plum Gut (passage between Orient Point and Plum Island)
  3. Block Island

Watch this video to see how the currents flow at these locations during Thursday and Friday:

Long Island Sound


Model Facts

  1. Resolution - 110m
  2. Time steps - 30min
  3. File size - 79MB per 24hrs
  4. Area covered - custom, to cover the Vineyard Race Course
  5. GRIB files available
  6. Tested in Expedition and Adrena, not tested yet in other software, but it should work fine.

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Model Construction

High quality bathymetry (depth information) is fundamental to model accuracy and thanks to NOAA's National Centers for Environmental Information, we have obtained some of the highest resolution bathymetry we have ever seen, down to 3m resolution in places.Long Island Sound Bathy

There are many complex, shallow inlets and rivers across the model area - intertidal areas where the seabed covers and uncovers with the tide. Previously, these areas were not well represented in bathymetric datasets due to the difficulty of measuring the depth in very shallow water by boat, with sonar. LIDAR has solved this problem, and now bathymetric measurements in intertidal locations are made from the air by overflying the area in a light plane equipped with LIDAR. 

Several bathymetric sources were harmonised, merged and resampled to a 0.001 deg (110m) resolution grid. This is used as one of the inputs to our modelling system and the model is run on one of our High-Performance Computers.


We have compared the model to the few available observations. Two examples that illustrate agreement to within 90% in timing and magnitude are the Newport tidal water level and The Race tidal current (location 41d13.69N 72d03.75W).


The 'observations' (blue) come from the NOAA Ports website (https://tidesandcurrents.noaa.gov/). The model is very new, and we have a lot of optimisation still to do; however, we are delighted with these early results.


We have been pushing hard to release the GRIB files before the Race on Friday, but we have had some technical challenges. 

Here is a GRIB file (free) to get you started, which covers Thursday from 2000 EST until Friday 2000 EST

You can expect GRIB files for SAT, SUN and MON after 2000 EST on Thursday 3rd Sept.

How to get GRIBS

    1. Purchase an advanced subscription
    2. Download GRIBs from our website (at the very bottom of the /data page) or via Expedition software

LIS - dataLIS_Exp


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Topics: currents, Expedition, sailing, yacht, racing, optimised route, high resolution model, grib, yacht race, Vineyard Race

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