Archive for August, 2011

August in review
August 31, 2011

By Meteorologist Mike Skurko

August delivered a break from the summertime heat across western Massachusetts.  We only hit the 90-degree mark once (92 on Aug. 1), while we typically average four 90-degree days in August.  Our average high temperature was 82.2 degrees this month, about a half-degree below average.  That was balanced out by the low temperatures though.  Our average low this month was 62.1 degrees, which is nearly a full degree above average.

The rain totals were excessive this month, even before Tropical Storm Irene hit.  We had a total of 11.67 inches of rain this month at Bradley Int’l.  However, if you subtract the 5.20 inches that Irene delivered there, this still leaves us with 6.47 inches of rain for the rest of August.  This by itself is about 160% of our normal August rainfall total (3.93 inches).

[Source: Bradley Int’l.]

Flood warnings end soon
August 30, 2011

By Meteorologist Mike Skurko

A Flood Warning remains in effect for Franklin, Hampden, and Hampshire County, but we may expect those warnings to be dropped tomorrow.  The Connecticut River has already reached its peak very early this morning, and it will continue its steady decline from here on out.

Below is a graph from the Advanced Hydrologic Prediction Service (AHPS), a forecasting branch of the National Weather Service.  This represents the past and projected levels of the Connecticut River at Northampton.  As you can see, it crested above flood stage at 1117.16 feet on Monday night.  As of 7 PM tonight it is sitting at 115.01 feet, and is forecasted to fall below flood stage (into the yellow “Action Stage”) at about 7 AM Wednesday morning.

AHPS provides these graphs for 13 different points in western Massachusetts, including 5 for the Connecticut River from Montague to Springfield.  All points along the Connecticut River are expected to similarly drop below flood stage by Wednesday morning, which is why the Flood Warnings may get dropped sometime tomorrow.

Irene’s rainfall totals
August 29, 2011

By Meteorologist Mike Skurko

The following is a list of rainfall reports across western Massachusetts from Tropical Storm Irene, compiled by the National Weather Service.  The most substantial amounts were clearly along the eastern slopes of the Berkshires, especially the western parts of Franklin County.

Franklin County
Conway 9.92″
Ashfield 9.75″
Shelburne Falls 8.50″
Heath 7.70″
East Charlemont 7.60″
Rowe 7.50″
Charlemont 6.48″
Leverett 4.37″
Orange 4.29″
Whately 4.00″
Sunderland 3.56″

Hampden County
Tolland 7.90″
Granville 7.68″
Southwick 7.39″
Westfield 5.88″
Agawam 4.08″
Monson 3.75″

Hampshire County
Goshen 7.50″
Plainfield 7.50″
Westhampton 7.15″
Worthington 6.45″
Ware 6.20″
Haydenville 5.92″
Easthampton 5.31″
Northampton 4.56″
Amherst 3.67″

Berkshire County
Savoy 9.10″
Clarksburg 6.00″
Becket 5.70″
Dalton 5.36″
North Adams 5.10″
Williamstown 4.90″
Pittsfield 4.71″

Watches/Warnings coming soon
August 25, 2011

By Meteorologist Mike Skurko

A few hours ago, hurricane watches were placed along the Atlantic coast from Virginia to New Jersey (see map below).  It is very likely that tropical storm or hurricane watches will be in place for parts of New England tomorrow.  This does not necessarily mean the forecast is changing…we are just getting closer to the onset of Irene.

Hurricane Warning – hurricane conditions expected in the next 36 hours

Hurricane Watch – hurricane conditions possible in the next 48 hours

Tropical Storm Warning – tropical storm conditions expected in the next 36 hours

Tropical Storm Watch – tropical storm conditions possible in the next 48 hours

With Irene expected to be moving through New England by Sunday night, it is very likely that a watch will be issued on Friday night (since it would be within 48 hours of the storm).  If these watches get upgraded to warnings, it doesn’t necessarily mean the storm is going to be worse.  If New England was upgraded to a warning on Saturday morning, that may simply suggest that we are now within that 36-hour window of the beginning of the storm.

The Saffir-Simpson Scale
August 24, 2011

By Meteorologist Mike Skurko

All hurricanes are categorized by the Saffir-Simpson scale, which measures the maximum sustained winds of the storm.  These winds are not found throughout the entire hurricane, they are found within the narrow eye wall of the storm.   Engineer Herbert Saffir and meteorologist Bob Simpson (who served as director of the National Hurricane Center) debuted this scale in 1973 to help categorize the potential impacts/damages of storms for the general public to more easily interpret.

While this scale is explicit in how a hurricane is categorized, it does have its limitations.  The Saffir-Simpson scale does not directly take into consideration flooding effects, storm surge, rainfall, or size of the storm.  Population densities, coastal layouts, and structure durability also have great impacts on how much damage a storm causes.  This is different than the Fujita scale, which measures tornadoes, as tornadoes are classified only after assessing the damage.

Because of these variables, hurricanes from a weaker category can often cause more damage than storms from a stronger category.  The best example of this is Hurricane Katrina, which made landfall only as a category 3 hurricane.  Likewise, a category 3 hurricane hitting a place like downtown Miami would potentially cause more destruction than a category 4 hurricane hitting a more rural part of the Gulf Coast.

Central Virginia Seismic Zone
August 23, 2011

By Meteorologist Mike Skurko

Western Massachusetts rarely feels earthquake tremors like it did this afternoon, but believe it or not, central Virginia is an area with more frequent seismic activity.  The epicenter of this magnitude 5.9 earthquake was near the town of Mineral, VA, which is about 40 miles northwest of Richmond…and about 80 miles outside Washington, DC.  The area of Mineral, VA falls near the Central Virginia Seismic Zone, as shown on the map below in yellow (#2653).

This is a zone classified by the U.S. Geological Survey (USGS) that has documented seismic activity dating back to the 1770s.  More specifically, it is known as an “area of Quaternary deformation and liquefaction.”  The term Quaternary is a geological term that specifies a period of 1.6 million years.  According to the USGS, these Quaternary zones and fault lines are believed to have registered an earthquake of magnitude 6.0 or greater in the last 1.6 million years.

Now we obviously do not have specific records and accounts from that long ago, just scientific evidence and analysis by experts.  We do have records from as early as 1774 from witnesses to an apparent minor earthquake in that area.  This area has continuously recorded a very small, non-damaging earthquake about every one or two years.  The largest earthquake (until today) from that zone registered as a magnitude 4.8 and occurred in the late 1800s.  Today’s magnitude 5.8 earthquake was literally ten times stronger.

[The Richter scale is an exponential scale…one step in magnitude equals a 10-times greater earthquake.  A magnitude 6.0 earthquake is ten times larger than a magnitude 5.0, and a magnitude 5.0 is ten times larger than a magnitude 4.0, etc.  The largest earthquake recorded in the U.S. was a magnitude 9.2 near Anchorage, Alaska in 1964.  The 1989 San Francisco earthquake was a magnitude 6.9]

The tremors from today’s earthquake were felt up and down the eastern United States from Maine to Alabama.  Below is a seismograph from the Weston Observatory in Boston.  A seismograph measures the vibrations in the ground…a larger vibration causes a larger jump in the needle.  On this graph, each colored horizontal line represents one hour.  The chart records one hour of activity and then moves down to the next line (think about how a typewriter works, it fills one line then returns and jumps down to the next).  The last red line near the bottom charted the activity for the one o’clock hour this afternoon.  You can easily see the spike in activity that occurs near the end of the line at about 1:53 PM EDT.  This is very close to when the earthquake also occurred in Virginia, nearly 500 miles away.

Tracking Hurricane Irene
August 22, 2011

By Meteorologist Mike Skurko

Hurricane Irene will continue making headlines as it starts to swing up the Atlantic Coast for the second-half of the week.  It may intensify to a major hurricane (category 3 or higher) shortly after moving through the Bahamas.  The latest outlook from the National Hurricane Center has Irene making landfall near Myrtle Beach, SC on Saturday morning.

It will also likely have some impact on New England.  Saturday night and through the day on Sunday, the Northeast may be getting soaked with rain showers from the remnants of Irene.  In fact, one model run totaled 6.25 inches of rain for Springfield this weekend.    However, there still is some uncertainty with it only being Monday.

Below are three examples of 3 different computer models forecasting the location of this storm at 8AM Sunday.  The larger image comes from a model (the ECMWF) that seems to correlate best with the National Hurricane Center’s forecast of a South Carolina landfall.  The storm dissipates moving up the I-95 corridor, but will still produce widespread, steady rain throughout the Northeast.  The two smaller images below are two different models, and they show Irene staying well off to the east, and possibly giving the Cape a bigger blow.  As you can see, it will take a few more days to fully understand where Irene will go and what it’s impacts will be.

 

Season’s first hurricane?
August 20, 2011

By Meteorologist Mike Skurko

We may get our first hurricane of the year with the formation of Irene earlier this evening.  While it is expected to stay a tropical storm for most of its journey through the Caribbean, the latest forecast from the National Hurricane Center has it briefly strengthening to hurricane status before hitting the Dominican Republic.

This hurricane season has been historic…namely for the lack of hurricanes so far.  For the first time in recorded history, none of the first seven tropical storms in the Atlantic achieved hurricane strength.  Tropical storm Irene, our ninth storm this year, may break that streak on Monday.

This is also a storm that may be making headlines in Florida later in the week.  The graphic below shows the expected path of Irene from the National Hurricane Center.  The green line represents its expected path, with a margin of error that shown in the gray forecast fan.  It still has a way to go…some models have it hitting Alabama, some have it pulling east up the Atlantic coast instead.  We’ll have to wait and see what happens.  Either way, southern Florida will likely be preparing for the effects of a tropical storm getting close on Thursday.

Hurricane/tropical storm classification
August 19, 2011

By Meteorologist Mike Skurko

Tropical Storm Harvey was named today, becoming this season’s eight named storm.  Regarding one of our earlier weather blog posts, it does not appear that Harvey will turn into this year’s first Atlantic hurricane.  It is expected to remain a tropical storm as it moves westward and makes landfall in Belize tomorrow afternoon.

Whether a storm is classified as a tropical storm or a hurricane is determined solely by wind speeds.  A system usually starts as a tropical depression, which is given a number (“Tropical Depression Eight”).  Once its maximum sustained wind speeds reach 39 mph, and it is upgraded to a tropical storm and given a name (“Harvey”).  Once the winds get above 73 mph, the tropical storm is upgraded to a hurricane.

The most intense hurricane is a category 5, which has wind speeds above 156 mph.  These classifications based on wind speeds (known as the Saffir-Simpson Scale) can be a little misleading.  The amount of damage caused is reliant on many other variables.  The three costliest hurricanes in recorded history were Katrina (category 3 when it made landfall), Andrew (category 5), and Ike (category 2).

Hurricane Hunters
August 18, 2011

By Meteorologist Mike Skurko

With the peak of hurricane season underway, it’s time to brush up on our knowledge about the tropics.  First thing’s first…before anything is classified as a tropical system, there is one important characteristic it must have.  The area of developing storms in question must have a well-defined closed circulation at the surface.  In other words, it must have that classic “swirling” and “spinning” feature to it.

For a tropical system in its infant stage, that circulation may not be as apparent as a mature hurricane.  The weaker the storm is, the weaker this rotation appears to be.  Detailed observations and direct measurements can establish if the rotation is there…such is the job for the “Hurricane Hunters”.

Special aircrafts known as “Hurricane Hunters” fly right into the heart of the storm, equipped with special instruments and a team of meteorologists to find signs of a circulation.  Today, a disturbance near the Cayman Islands was expected to be investigated, but technical precautions kept the Hurricane Hunters flight grounded.  Meteorologists from the National Hurricane Center in Florida remain optimistic that this disturbance will be upgraded to a tropical depression in the next day or two, but confirmation from the Hurricane Hunters will wait until tomorrow.