Tag Archives: atlantic hurricanes

NYC Halloween/Marathon/World Series Weekend Weather, Sandy Retrospective – Oct 30, 2015

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After a brief warmup mid-week, we return to more seasonable fall weather for the weekend. Luckily, it appears that this weekend should be rain free, providing excellent conditions for Halloween revelers, Mets fans, and NYC Marathon runners alike. It was quite a different story 3 years ago this weekend, when the city and indeed the entire region was just beginning to comprehend the scope and magnitude of the destruction wrought by a once in 500 year storm: Hurricane Sandy.

Rest of today – sunny, with a high right around average at 60ºF. It will be a chilly evening with lows in the 40s. Temperatures during game time at Citi Field should be in the low-50s.

Saturday – cooler, with highs in the mid-50s, but again with plenty of sun with high pressure in the vicinity. Temperatures for trick-or-treaters out there should again be in the low-50s range tomorrow afternoon and early evening. Weather for World Series game 4 should also be in that low-50s range.

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Sunday – AM temperatures should at race time for the marathon should be hovering right around the 50ºF mark with only a light wind. High temperatures warm up into the low-60s later in the day with a warm front moving through. Temperatures won’t cool off that much during the early evening hours, so if the Mets do make it to game 5, conditions should be good for viewing the game. There is only a slight chance for showers overnight into Sunday.

Monday – clouds and sun on Monday with temperatures climbing into the low-mid 60s.

 

Hurricane Sandy Retrospective

Yesterday marked the 3-year anniversary of Hurricane Sandy’s landfall on the central New Jersey coast. Sandy was in many ways a uniquely devastating force of nature: as it matured, it’s size ballooned, allowing for it to push up a significant storm surge ahead of it. Unlike most mature tropical cyclones that reach the mid-latitudes, Sandy did not recurve out to sea and spare the East Coast. At these latitudes, the predominant wind patterns are from the west (the westerlies), and there’s usually a cold front that pushes tropical cyclones to the east. In Sandy’s case, a low pressure system to its northwest actually produced the opposite effect: Sandy was pulled to the northwest along the counterclockwise cyclonic flow around that low pressure system. This resulted in a historic landfall on costal New Jersey. As the forecast models came into consensus on this result, I began to fear for the worst. Because Hurricane Irene had passed the previous year with great hype, but minimal damage, I had a bad feeling that many New Yorkers would not heed the warnings about this monster storm, even though there was high confidence in an historic event about to unfold.

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A monster storm

Sandy’s landfall also coincided with a supermoon high-tide, which meant that its already significant storm surge was augmented that much more by the pull of the moon. This resulted in catastrophic storm surge inundation along a vast expanse of the Northeast. The geology and bathymetry of New York Harbor made it all the more susceptible to storm surge, as its funnel shape served to channel and amplify Sandy’s storm surge. The fact that Sandy made its land fall to the south of New York meant that its most damaging northeast quadrant (Northern Hemisphere cyclones get a boost in the northeast quadrant because the direction of winds in that quadrant coincide with the direction of the Earth’s Coriolis force) hit the city dead on. A record-breaking storm tied of 14 feet was recorded at The Battery in Manhattan, smashing the previous record of 10 feet.

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Scenes of utter destruction like the one below were commonplace. Over 100 deaths were recorded, with areas like Staten Island’s east coast and the Rockaways particularly badly hit. The costs of the damage ran over $60 billion dollars. To this day, many people’s lives still have not returned to normal, many are still not able to move back into their homes.

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On a personal level, I was very fortunate to be in a neighborhood that was left high and dry, and crucially with power. Along with thousands of other New Yorkers, I felt an urgent and compelling need to get out on the ground and help our neighbors who were hardest hit and who had lost so much. My wife, who had just started working at a new school, found out that week that one of her coworkers had been killed – crushed by a fallen tree – during the storm. My volunteer work after the storm took me to many areas of New York City that I had not explored before. I saw witnessed scenes that I will never forget. For me, this day will always entail with it a sense of grieving, and will alway serve as a reminder to remain vigilant, because the storm that we never thought would happen here did – and could again.

Hurricane Joaquin Update – Oct 2, 2015

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Good news to report regarding Hurricane Joaquin – since yesterday, forecast models have arrived at a much clearer consensus regarding the track of Joaquin once it leaves the Bahamas – and the resulting forecast track takes it well east of the US East Coast.

This means we will luckily miss any severe impacts from a landfalling tropical cyclone. However, with Joaquin to the south and a ridge of high pressure to the north, continuous onshore northeasterly winds will still present moderate coastal flooding issues. Temperatures will likewise remain cool under the clouds and onshore flow, with rain expected to continue from today until Saturday. Lingering showers may persists on Sunday.

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Tropical Depression One Update – Jul 1, 2014

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Overnight, the area of disturbed weather mentioned in my previous post intensified enough that the National Hurricane Center upgraded the storm to the 2014 Atlantic Hurricane Season’s first tropical depression.

As you can see below in a satellite image captured at 7:45AM EDT this morning, TD One is showing increasing signs of organization. You can clearly see overshooting tops (the bubbly looking clumps of clouds), which are clouds that are breaking up through the tropopause and into the lower stratosphere. This is a hallmark sign of intense thunderstorm updrafts, where warm, humid air is rapidly moving upwards in the atmosphere. You can even see the beginning of what may eventually become a spiral band forming directly south of the storm’s center.

National Hurricane Center has issued tropical storm warnings for the Eastern Florida coast. TD One’s sustained wind speeds are at 35mph, only 4mph shy of tropical storm criteria. In fact, as of this writing, TD One may have already become Tropical Storm Arthur, our first named storm of the 2014 Atlantic Hurricane Season.

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Storm Track Forecast

TD One is forecast to begin a turn towards the north, then northeast over the period of the next day or so. Thereafter, it is forecast to steadily accelerate in forward speed towards the northeast as a cold front currently approaching our region from the west begins to steer the storm. It appears in the latest model runs that the storm may make a landfall in the Cape Hatteras area of North Carolina, and the move offshore of the Northeast Friday night into Saturday.

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Intensity Forecast

Although the strongest thunderstorms are currently confined to the southern half of the storm, there is high confidence that the storm will continue to organize and become a tropical storm shortly. The National Hurricane Center is also now forecasting that TD One will have sufficiently good conditions to strengthen into a weak hurricane by the time it makes its closest approach to North Carolina. It will eventually get absorbed by the cold front mentioned above and make an extratropical transition somewhere off the coast of the Canadian Maritimes.

What This Means for Us

The tropical moisture from this storm is increasingly likely to throw a damper on July 4th plans for the area, when the storm and approaching cold front will interact to produce the chance for heavy rain, thunderstorms, and possibly some strong wind gusts. However, even though this is forecast to occur within the next 3-4 days, there is still a good deal of uncertainty as to the final track of this storm, especially as it approaches the Northeast. More updates soon!

2014 Atlantic Hurricane Season Outlook – Jun 2, 2014

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Yesterday marked the official start to the 2014  Atlantic Hurricane season (June 1 – November 30), so this is as good a day as any to talk about the forecast for this season. The graphic below shows the National Hurricane Center’s official 2014 Hurricane Season Outlook that was released last month. This forecast is probabilistic, i.e. it gives a range of numbers and chances that this season will either exceed or fall below the forecast total.

National Weather Service National Hurricane Center's forecast summary for 2014
National Weather Service National Hurricane Center’s forecast summary for 2014

Explanation

In the NHC’s parlance, Named Storms refers to tropical or subtropical storms that produce sustained winds in excess of 39mph (this is the criteria for a tropical or subtropical storm) at any point in their life cycle. Hurricanes refer to the named storms that end up producing sustained winds in excess of 74mph, and Major Hurricanes refer to hurricanes that make it to Category 3 or higher on the Saffir-Simpson classification scale. Accumulated Cyclone Energy (ACE) is a rough measure for the overall intensity of a tropical cyclone and is calculated as follows:

The ACE of a season is calculated by summing the squares of the estimated maximum sustained velocity of every active tropical storm (wind speed 35 knots (65 km/h) or higher), at six-hour intervals. Since the calculation is sensitive to the starting point of the six-hour intervals, the convention is to use 0000, 0600, 1200, and 1800 UTC. If any storms of a season happen to cross years, the storm’s ACE counts for the previous year.[2] The numbers are usually divided by 10,000 to make them more manageable. The unit of ACE is 104kn2, and for use as an index the unit is assumed. Thus:

\text{ACE} = 10^{-4} \sum v_\max^2

where vmax is estimated sustained wind speed in knots. (Source – Wikipedia)

Hence, a high ACE number corresponds to a very intense storm or storm(s).

Outlook

As you can see from the above image, the NHC is calling for a normal to slightly below normal season for the Atlantic with 8-13 named storms, 3-6 hurricanes, and 1-2 major hurricanes. Despite the fact that the forecast calls for a normal to below normal season, it only takes one landfalling hurricane or major hurricane to inflict serious damage to a coastal area. Even with just tropical storms, huge amounts of rain can fall leading to major flooding.

El Niño’s Impact

One of the reasons why the forecast is calling for a normal to below normal season is that it appears an El Niño event is initiating and forecast to increase in intensity. El Niño refers to a phenomenon that occurs when the ocean surface of the Eastern Pacific Ocean becomes abnormally warm (La Niña refers to the opposite effect, when the Eastern Pacific cools abnormally).

This anomalous warming of the Eastern Pacific leads to all sorts of global climate impacts. Among these is a noticeable decrease in the incidence of Atlantic hurricanes, and an increase in the number of Eastern Pacific hurricanes. In fact, you can see in the same outlook, NHC is calling for a near normal to above normal hurricane season for both the Eastern and Central Pacific. The reason behind this is simple: hurricanes feed on heat to grow, so the warmer the water below a storm, the greater the potential for that storm to grow.

Map of sea surface temperature anomalies as of 6/2/2014
Map of sea surface temperature anomalies as of 6/2/2014

As you can see from the map above, there is a region of abnormally warm sea surface temperatures extending west into the Eastern Pacific from the coast of Ecuador and Peru (yellow & orange). At the same time, there is a large area of much cooler than normal sea surface temperatures extending from the west coast of Africa into the Central Atlantic (light and dark blue). Incidentally, these cool temperatures off the coast of Africa are in a region that is notable for spawning some of the strongest hurricanes, the Cape Verde type hurricane. Clearly, if this temperature anomaly keeps up, it will serve to inhibit the formation of tropical storms and hurricanes in that region.