Tuesday, September 18, 2018

Tuesday Evening Weather Update

The heavy rainfall from Tuesday morning and afternoon has come to an end with only a few light showers and sprinkles remaining Tuesday evening.  Under mostly cloudy skies temperatures will remain in the low 60's during the overnight.  Unfortunately highs didn't warm as much as hoped, staying in the upper 60's and low 70's Tuesday afternoon. 

While most of the night will remain dry, showers and thunderstorms will move back in Wednesday with the arrival of an upper level disturbance.  Rain and thunderstorms should increase in coverage through late morning and early afternoon Wednesday.

Rainfall totals Tuesday ranged anywhere from a quarter of an inch, all the way to an inch in some spots.  Additional rainfall Wednesday and Thursday may bring another one to two inches for northern Illinois and southern Wisconsin, with higher amounts to the northwest in Iowa and Minnesota.

A Rainy Few Days

Showers and thunderstorms have been moving throughout the area all morning. This rain is associated with a cold front that will slowly dip down into our neck of the woods. As it slowly slides south, more rain is expected throughout the rest of the day, Wednesday, Thursday and early Friday. The heaviest rain will fall off to our west and north.

Meteorological fall began on September 1st, but the Autumn Equinox falls this Saturday at 8:54pm. Temperatures to start off the fall season will be seasonable. High temperatures Friday and into the weekend will be in the lower 70s, which is right where we should be for this time of the year.

Monday, September 17, 2018

Dry Stretch Comes To An End

It's been a copy and paste forecast for over the last week. Our dry stretch of sunny days will be coming to an end after today. When today is all said and done, we will have went the last 10 days without any rainfall.

Not only will the dry stretch be coming to an end, but also the above average temperatures. Today we will see highs top out in the upper 80s to near 90 degrees.

Tuesday and Wednesday will be in the upper 70s and lower 80s. Thursday we will briefly bounce back into the mid 80s, but going into Friday and the weekend we will back down around average. Our average for this time of the year should be in the mid to low 70s.

Late tonight we will begin to see the chance for an isolated shower return to the forecast. Scattered showers and thunderstorms will be possible Tuesday, and more likely going into Wednesday and Thursday.

The rain this week will be nothing compared to the rain that Hurricane Florence dumped over North Carolina. Swansboro, NC picked up 33.90", as of Sunday 9/16/18 at 2pm. That sets a record for the highest amount of rainfall from a tropical disturbance in North Carolina.

Sunday, September 16, 2018

Mid-August Warmth in Mid-September

It was a steamy September weekend with temperatures Friday, Saturday and Sunday warming into the mid and upper 80's, with a heat index in the low 90's.  More of the same is in store Monday with temperatures warming into the upper 80's and the heat index in the low 90's.  Average highs for mid-September should be in the middle 70's. 

Tuesday will be humid but there will be an increasing chance for rain and thunderstorms by the afternoon and evening with the arrival of a cold front.  The front will briefly bring temperatures into the upper 70's Wednesday, but temperatures will
warm right back into the upper 80's Thursday.  An even stronger cold front will move through late Thursday finally bringing temperatures back down where they should be, mid 70's, for the upcoming weekend. 

A blocking pattern in the atmosphere, a result of Hurricane Florence making landfall in the southeast, has kept the jet stream buckled north over the High Plains and Midwest.  Hurricanes are a great source of energy and can release a lot of heat back into the atmosphere.  Often times with
tropical systems that make landfall the atmosphere tends to warm further upstream.  But now that the storm has weakened it'll become 'caught up' within the jet stream, quickly moving into the northeast this week.  This will allow the jet stream to shift a little further south, bringing an end to the late summer warmth and a return of rain towards the middle of the week.

Friday, September 14, 2018

Hurricane Florence Has Made Landfall

At 7:15 am EDT (6:15am CDT), Hurricane Florence officially made landfall near Wrightsville Beach, NC.

While at its strongest Florence was once a Category 4 hurricane, but when it made landfall Friday morning it was a strong Category 1 hurricane with winds around 90 mph. Florence continues to slowly move slowly inland at 6 mph. Due to the slow progress, it will dump upwards of 20+ inches of rain in portions of North and South Carolina by the time it is all said and done.

Not only is the amount of rainfall a concern, but also the storm surge associated with Florence. On average storm surge levels will be between 6-9'. 

In New Bern, NC they saw near 10' storm surges that left over 100 residents stranded, according to the city's office of public information.

Wednesday, September 12, 2018

7am Hurricane Florence Update

As of the 5am EDT advisory, Hurricane Florence remains a Category 4 storm, but Florence's maximum sustained winds have weakened slightly to 130 mph. As it moves through even warmer waters, the potential remains for some strengthening. However, as Florence begins to come into contact with the Carolina coast and southwesterly wind shear it will begin to weaken. It is important to not focus on the foretasted track line and the entire cone of uncertainty because Florence could make landfall anywhere within the cone.

As a result of a blocking high pressure system over the Mid-Atlantic, it will slow Hurricane Florence down. In the end, the high will cause it to stall over the North Carolina, South Carolina and Georgia.
As Hurricane Florence stalls out over the Southeast, rainfall totals will range anywhere from 4-15" and could locally top out upwards of 20+" of rain. Early next week, Florence is foretasted to slide north. Then a cold front that will bring us scattered showers early next week will help push the remnants of Florence back out to sea.

Tuesday, September 11, 2018

Hurricane Florence: 8:00 PM Tuesday Update

As of 7:00 PM CDT, Hurricane Florence remains a Category 4 Hurricane with sustained winds of 140 mph and gusts up to 165 mph. Her pressure has risen slightly to 945 mbs, which indicates that she is a little weaker than she was earlier today, but that does not mean that Florence is ready to completely weaken yet. In fact, she will likely intensify a bit more tonight and through the day tomorrow, before she finally does begin to weaken a little bit.

Florence is also moving at a pretty good speed for a hurricane: west-northwest at 17 mph. Florence is rounding the base of a high pressure over Bermuda, which is partially the reason she is traveling at that current speed. However, while Florence may be moving fast now, she will begin to slow down as she nears land, and this will play a notable impact on her intensity.

As Florence nears land on Thursday, she will begin to slow down as an area of high pressure sits across the Great Lakes Region. This means that Florence will have to change her course slightly, but her forward momentum (and other atmospheric conditions) will want her to move forward instead of simply turning. What this means is that Florence will effectively hit the brakes as she nears land on Thursday, causing her effects to be felt along the coastline well before she actually makes landfall.

When a hurricane sits over waters for a long enough time, it begins to cause problems for itself. By slowing down, a hurricane will expose itself to cooler waters churned up by it's own surf. Hurricanes love warm waters, and part of the reason Florence is as strong as she is right now is because she is sitting over warm waters. As she slows down, she will cause the waters below her to cool a bit, and this will impact her intensity.

Also expected to be against her will be the presence of wind shear (that is, change of wind direction with height and speed) as she nears the coastline. Hurricanes like an atmosphere with little wind shear, and currently she is in an environment with little wind shear. But closer to the shore, Florence is expected to encounter shear from a high pressure over the Great Lakes, as well as a stalled out frontal boundary just a little bit inland.

What do all of these factors mean for Florence? Simple, it means that she may actually weaken before she reaches land, potentially down to a Category 3 Hurricane.

What are the impacts that the North Carolina coastline faces? First off, let us talk about the winds: perhaps the most misunderstood event of a landfalling hurricane is the wind speeds. The strongest of winds are located in the eyewall of a hurricane, which is usually found about 40 miles away from the center of the hurricane. Within the eyewall, that is where you will find the 140 mph winds. Once Florence reaches land, however; she will rapidly weaken (as most hurricanes do). This means that places further away from the shoreline will not be seeing 140 mph winds at all. In fact, most places effected by the hurricane will not be seeing 140 mph winds, and only about a third will actually see hurricane force winds. In addition, the strongest winds will likely be along the shoreline, this is because water offers less friction for air than land (i.e., water does not slow wind down as much as land does).

Due to Florence's expected brake slamming late tomorrow night/Thursday, perhaps the most general threat will be several places along the coastline may experiencing rain fall well in advance of her landfall. In fact, it is entirely possible that over 15 inches of rain could fall in certain locations (with locally higher amounts) by the time that the entire event is over. That means that flooding is going to be a concern.

Storm surges will also be a threat along the immediate shoreline, with expected storm surges of 6-9 feet in some locations. Storm surge is effectively the wind pushing water inland, causing flooding of it's own separate from the rain.

Another potential impact are tornadoes, which is a common hazard with most hurricanes, especially major hurricanes. Lots of low level shear caused by the hurricane's rotation itself can cause thunderstorms in the rain bands to rotate, and sometimes they produce tornadoes. Hurricane Ivan in 2004 produced the most tornadoes from a hurricane numbering 120 confirmed tornadoes, but most hurricanes do not produce that many tornadoes, usually they produce a dozen or so and usually the tornadoes stay below EF3 intensity. Nonetheless, they are still a possibility.

The next update will be between 10:30 PM and 11:30 PM CDT.

-Timothy Albertson