With nearly 2 weeks provisioning and readying Kailoa for our first leg south our thoughts have turned to picking a weather window for departure. We have been watching the weather every day for the last 2 weeks and have estimated that the best departure window is tomorrow (Sunday) at 0700. We have no choice but to make this leg outside instead of making passage through the inland water way. This is because our mast height is 67 ft and all the bridges crossing the inland waterway are 65 ft or lower.
Our first leg will be an ocean passage from Hampton, VA to Ocracoke, NC, or a travel distance of approx. 160 NM. To travel south we need a weather window with sustained winds out of the west, north or east during the anticipated travel time. We assume that we will be cruising at 7 knots on average which translates to a travel window of about 24 hours to reach our intended destination. To make these decisions we rely on a variety of weather applications including PredictWind, Windy, Outcast, and the National Oceanographic and Atmospheric Administration (NOAA) weather service.
The PredictWind application is a free software program that provides marine weather forecasts and tools for sailing yachts embarking on coastal cruising and offshore passage making. The model uses data from a variety of regional forecast models with different strengths and weaknesses that provides predictions of winds, wave, tide and ocean current. Animated visual output helps mariners determine optimal departure times, course routing and expected conditions on route. The output also includes a visual summary with tables based on 4 sets of models that predict wind direction, speed, typical sea conditions, including the distribution of wave height and direction at a specific location.
The weather predictions have more certainty 1 to 2 days in advance of the planned departure and less certainty 3 to 5 days in advance of planned departure. The bottom line is that the departure time ends up being a game-day call. We learned from a meteorologist, Eric Nordberg, that the wind speed predictions are at an elevation of 10 meters above sea level which means that the observed conditions at the sea surface are about 20% higher than the average condition predicted by the models. To compensate for this, we always look at the predicted wind speed of gusts. Because these models are regional, they don’t always predict the conditions encountered on route. Since it’s just the 2 of us we like to err on the conservative side in decision making for round the clock offshore passages.
To decide when to depart we use 4 PredictWind models in a weight of evidence approach:
PWE – PredictWind proprietary weather model that uses US National Weather Service, National Centers for Environmental Prediction, global initial conditions.
PWG – PredictWind proprietary weather model that uses European Centre for Medium-Range Weather Forecasts (ECMWF) which is an independent intergovernmental organization supported by 35 states.
ECMWF – European Center for Medium-Range Weather Forecasts and is highly regarded by Meteorologists and top Navigators around the world. The ECMWF High-RES model consistently rates as the top global weather model from a national weather service with the highest rating scores.
GFS 27– Global Forecast System from National Centers for Environmental Prediction which is used by most other weather websites/apps. PredictWind uses the GFS-FV3 model which is a significant upgrade to GFS in about 40 years.
Mariners need to be aware that the models update at different frequencies or either 6 or 12 hours which may provide a range of results that need to be interpreted and can lead to confusion.
We have been experiencing high wind (gusts to 40 knots) here at Hampton for the last few days that are expected to lie down tonight. After analysis we determined that there is a good window for departure Sunday morning around 0700. Clear skies are predicted along with sustained winds out of the west at about 10 knots (gusts less than 20 knots) and temps between 40 and 60 °F. The figure below is a screen shot of the PredictWind visualization of the trip today versus tomorrow. Red-orange is high wind and yellow-green is low wind.
The trip plan includes a motor-sailing passage east out of the Chesapeake Bay past Norfolk VA, a turn south at Cape Henry toward Virginia Beach, a long run south along the barrier islands to Cape Hatteras. The final leg will include a turn southwest toward Ocracoke at Diamond Shoals off Hatteras. A summary of the waypoints and conditions expected along each leg is summarized below.
The model output worst case scenario, shown below, is that we would be on a reach or downwind for 80% of the trip and upwind for about 20% of the trip. The trip can be completed in about 24 hours with max winds of about 20 knots. NOAA predicts wave heights of 2 to 3 ft off Diamond Shoals Sunday night. We also looked at the position of the gulf stream current heading north which is running well offshore during the planned passage.
One of the tricky segments of the trip will be traveling upwind once we clear Diamond Shoals at night. With average wind speeds above 10 knots in the direction of travel it will likely be necessary to tack for about 35 miles upwind at night. We have accounted for a slower average boat speed to attain distance made good during this leg because we expect to be tacking which adds distance to the trip. Some of the models indicated that the wind lays down Monday morning and then picks up again in the afternoon. It will be important to get inside Ocracoke in the morning. The trip plan will enable us to gage how we are doing in real time relative to the plan. We will both be up during the day and keep watch in 3-hour shifts after 18:00.
We have looked beyond the planned passage as well and see that very heavy winds are predicted for Thursday, Thanksgiving. If all goes well, we will be able to depart Wednesday for Beaufort, NC and secure ourselves on a dock before the storm approaches. With all this planning we recognize that life is what happens after you make plans, and we will have adjust the sail plan accordingly based on what we encounter
Signing off for now as we make final preparations. More to come!!
PS: A shout out Happy Birthday to Scotts Brother Sandy who turns 80 on November 26th.
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