Tag Archives | Nor’easter

A Rough and Significant Winter

By Sage Lichtenwalner on March 22, 2013 in Visualizations

It has been a rough winter in New Jersey, especially on the coast. First, Post Tropical Storm Sandy struck Atlantic County on October 29th 2012, becoming the costliest natural disaster in New Jersey’s history. Over the next 5 months, several additional strong storms made their way across the state, bringing with them heavy winds, coastal and inland flooding and significant snowfalls.

Strong storms, many of which are called Nor’easters, are common occurrences in the Mid-Atlantic during winter months. Their strong winds also lead to high waves in the ocean. But this past winter was rather exceptional.

The above graph shows an analysis of wave heights measured by NDBC Station 44025. Each bar depicts the maximum wave height reached for each of the 12 largest events (each lasting 2-3 days) recorded over the past eight years (from January 2005 to today). Of the 12 events with the highest waves, 6 of them have been in the last 6 months. The largest recorded wave event was, of course, due to Sandy. The 12th largest occurred during the nor’easter that struck earlier this month.

It’s important to note that this does not (yet) represent a significant trend. Taking the top 20 events into account, only the same 6 events occurred this winter. Extreme events can often occur in spurts, triggered by prevailing climatic conditions, so the likelihood of many major events coinciding is not uncommon. In addition, an 8-year dataset is far too limited to make any assumptions about long-term climate changes.

However, it should be quite clear from this evidence that New Jersey residents are certainly ready for Spring, and more importantly, calmer weather.

Significant Waves

By Sage Lichtenwalner on March 15, 2013 in Visualizations

Last week a major snowstorm travelled across the continental United states, becoming a strong nor’easter over the Mid-Atlantic. While snowfall amounts in New Jersey were far less than some had predicted, the wind and waves that battered the coast were still quite severe. Dunes in Mantoloking, NJ that were heavily damaged last fall by Hurricane Sandy were again breached, causing flooding and further hindering repairs.

Wave heights at NOAA Station 44025, just 43 miles off the coast of New Jersey, reached 18.4 feet on the night of March 6th. The blue line above shows the significant wave heights measured by the NOAA buoy over the course of the last week.

The red horizontal lines signify the percentage of hourly wave measurements recorded between 2005 and 2012 that were less than the indicated height. The top line, at 31.6 feet, represents the maximum wave height reached during the 8-year record, which occurred as Hurricane Sandy made landfall.

The maximum wave height during last week’s storm reached the 99.9th percentile. Only 1 hourly measurement in 1000 hours of measurements (the equivalent of 42 days) ever reach this level. After the peak, wave heights remained between the 90 and 99.9th percentile for 3 days, which indicates the significance of this storm.

Matlab tip: If you’re interested in calculating significant wave heights at various percentile levels at other stations or for other parameters, here’s some code to play with.

% Load in the concatenated NDBC Datafile
fid=fopen('data/44025_8yr.txt','r');
data = textscan(fid,'%4f %2f %2f %2f %2f %f %f %f %f %f %f %f %f %f %f %f %f %f %*[^\n]','HeaderLines',2,'CommentStyle','#');
fclose(fid);
 
% Calculate time and remove bad datapoints
dtime = datenum(data{1},data{2},data{3},data{4},data{5},0);
wvht = data{9};
wvht(find(wvht==99)) = NaN;
 
% Calculate percentile levels and convert meters to feet
wvd = sort(wvht(find(~isnan(wvht))));
disp([.9 wvd(round(length(wvd)*.9))*3.28084]);
disp([.99 wvd(round(length(wvd)*.99))*3.28084]);
disp([.999 wvd(round(length(wvd)*.999))*3.28084]);
disp([1 wvd(round(length(wvd)*1))*3.28084]);

A Colorful Winter Storm

By Sage Lichtenwalner on March 8, 2013 in Visualizations

A major winter storm made its way across the continental United States this week, dropping snow across the Dakotas, then the Midwest and the Mid-Atlantic before finally heading out to sea over the Northeast. While snowfall from the storm was difficult to forecast precisely, nonetheless it still caused major damage across many states.

The image above shows what the storm looked like at 9am EST on March 8, 2013, through the false-color eyes of the AVHRR instrument on board satellite NOAA-16. Unfortunately, AVHRR was not designed to measure visible light as many more modern satellites do. It’s primarily used for measuring the surface temperature of land and the ocean. The colors in the above image were approximated with a computer algorithm that converted AVHRR’s red, near-infrared and infrared channels into red, green and blue, creating this non-traditional colorful image of the Mid-Atlantic.

While the colors in this image can not be regarded as real, they are still useful. The white clouds are colder and generally higher in the atmosphere, while yellow clouds are slightly warmer and lower. Most of the clouds connected with the storm system are yellow. Storm bands are also visible as semi-circles pushing in towards Massachusetts and on down into New Jersey. This counterclockwise rotation is a common feature of a Nor’easter.

In advance of the storm, scientists at Rutgers deployed an underwater glider to measure how the storm will mix sediment in coastal waters. The glider certainly saw a lot of action, as wave heights reached 14 feet at the New York Harbor entrance, 24 feet off the coast of Virginia Beach, and 30 feet at the Hudson Canyon as the storm’s center passed by late on March 6th.

Special thanks to Steve Miller at NRL-Monterey for the code used to create this image.

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Tag Archives | Nor’easter