Hurricane Joaquin is now in the same position as Sandy several days before it hit New York. Will Joaquin make a beeline from the Bahamas to the Big Apple?
Though there are similarities between the two atmospheric patterns, there are also differences.
Hurricane Sandy was embedded in a well-defined southerly flow and the forecast was straightforward: A developing trough in the eastern US would pick Sandy up and swing it into the coast.
Joaquin developed in a calm spot near the Bahamas and has drifted slowly for several days. Forecasts diverged on whether an approaching trough would pick it up.
At one time, the National Hurricane Center forecast had the hurricane crossing the North Carolina Outer Banks and heading up Chesapeake Bay to Washington.
Later forecasts, incorporating more data including extra balloon launches at many weather stations in the eastern US, began to suggest that the trough might not pick Joaquin up; the most reliable forecasts had a path well out to sea.
Now that Joaquin has stopped meandering and has begun a northward trek, the forecast of an out-to-sea path has been confirmed by the forecasting models.
Joaquin will not be another Sandy. But you don’t need a hurricane to get wind and rain — a lot of rain.
Joaquin Forms In A Hostile Atlantic: The Importance Of Wind Shear
A hurricane is fueled by the conversion of latent heat of evaporation to wind. Heat is bound up in the water molecules after they have been ripped from the ocean surface. The energy of this latent heat is released when the water molecules condense. However, the real driver of circulation in a hurricane is the outflow at high levels. This outflow lowers the pressure in the center and the pressure gradient increases, causing the high winds.
Vertical wind shear (change of wind with height) blows apart this vertical structure so that outflow is reduced and intensification is muted.
This summer has been characterized by unusually persistent vertical wind shear over most of the Atlantic Ocean. Juaquin found a small opening in the pattern where the wind shear was light and the storm rapidly developed. Juaquin has now reached its maximum strength with winds of 130 miles per hour. Increasing mid-level winds from the southwest will weaken the storm as it moves northeast.
Result Of A Slow Moving Hurricane: The Same Place Gets Affected For A LongTime
There’s no question that when a hurricane lingers over an area it’s worse for that area than if the hurricane rushes through. The central Bahamas have experienced sustained hurricane force winds for more than 36 hours from Joaquin. Damage has been extensive.
Result Of A Slow Moving Hurricane: Feedback Weakens The System –Usually
Over open ocean, the water temperature decreases with depth. When a hurricane stays in one place, it stirs up the water and mixes the cooler water below with the surface water. Cooler water means less available energy. But Joaquin is over the shallow uniformly-warm water of the Bahamas, so it has not been affected by upwelling of cold water.
No Repeat Of Sandy’s Forecasting Debacle
As Hurricane Sandy approached New York, the storm underwent a transition from tropical to extra-tropical. This is common when hurricanes move north into the zone of jet stream westerly winds. In the mid-latitudes, energy is transferred to wind from potential energy of contrasting air masses.
Just before Sandy reached New York, the National Weather Service deemed it an extra-tropical storm, and the National Hurricane Center discontinued issuing warnings. NOAA, which has jurisdiction over both the National Weather Service and the National Hurricane Center, learned its lesson. Warnings will continue whether the storm is deemed tropical or extra-tropical.
Joaquin Will Contribute To Coastal And Inland Flooding
As Joaquin moves north, it is bumping up against a huge high pressure center over eastern Canada. The increasing pressure gradient and the long fetch of wind will produce high waves along much of the US east coast. Many coastal communities are shoring up dunes in preparation. On some beaches, a considerable amount of sand was lost during last week’s prolonged spell of east winds.
A cold front moved just off the east coast early in the week and stalled. The entire eastern seaboard will get heavy rain west to the Appalachians due to ‘overrunning.’ When a cold front stalls, the denser cold air is hard to dislodge. If warm air tries to flow back, it is lifted and the lifting causes moisture to be squeezed out (rising air cools; cool air cannot hold as much moisture as warm).
The flow between Joaquin and the high pressure to the north has produced a stream of saturated air that will overrun the cold front through the weekend.
Very heavy rain, in some places totaling over ten inches, is forecast for the Carolinas.
Charleston, South Carolina At Risk
Charleston is a city virtually at sea level.
This situation is extremely dangerous, as the waves will push ocean water to street level, and the anticipated ten inches of rain will have nowhere to go.
The entire state of South Carolina is under a state of emergency, and coastal and flash flood advisories have been issued for Charleston.
Is There A Connection Between This Event And Global Warming?
As the oceans warm, less heat will be required to rip molecules loose; As the atmosphere warms, it can hold more moisture. These two factors, implicit in global warming, already seem to be providing more water vapor which is producing more rainfall worldwide. Record flooding in Texas, Oklahoma, Arizona, the midwest , and the Balkans this year suggests that climate change is, among other things, making the world wetter.