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.

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.

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.

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

Hurricane Florence: 5:00 PM Tuesday Update

As of 4:00 PM CDT, Hurricane Florence remains a Category 4 Hurricane, only now her winds are back up to 140 mph with gusts upwards of 165 mph. Hurricane Warnings are now in effect for most of the North Carolina shoreline, including areas around the Outer Banks and Wilmington, North Carolina, down to Myrtle Beach, South Carolina.

Hurricane Florence is moving quickly to the west-northwest at 17 mph, which is a pretty good speed for a hurricane. However, 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 her. She will expose herself to cooler waters churned up by her own surf, and this greatly effects a hurricane. 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 adding against her is the presence of wind shear as she nears the coastline. Hurricanes like an atmosphere with little wind shear (that is, change of wind direction with height and speed), and currently she is in an environment with little wind shear. However, as Florence moves closer to the shorelines, she will begin to encounter shearing from the high pressure over the Great Lakes, as well as a stalled out frontal boundary just a little bit inland.

What does this mean for Florence? Simple, it means that she may actually weaken before she reaches land. Florence will likely intensify a bit more tonight and likely during the day tomorrow. But then she begins to slow down, and combined with the shearing, she will begin to weaken a bit as she heads towards land.

Now, Florence is expected to sit not too far off the coastline from Thursday until she makes landfall on either late Friday Morning or early Friday Afternoon. This means that places along the coastline will be exposed to high surf, gusty winds (we will get to that topic in a moment) and heavy rains. This means that there is the possibility that many places could see a couple of inches of rain before Florence even makes a landfall.

The other thing to keep in mind is that not all of the North Carolina is going to be seeing 140 mph winds. In fact, only a small portion of the hurricane contains these winds, and they are located within an "eyewall". An eyewall is located generally 40 miles or so out from the center of the hurricane, and this is where the strongest winds from a hurricane can be found. As Florence weakens, her wind field may expand a little bit, but as is the case with most hurricanes, the hurricane force winds are limited to a relatively small area.

Other hazards from Hurricane Florence include 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. Nonetheless, they are still a possibility, and usually the tornadoes stay below EF3 intensity.

I will post further updates on Hurricane Florence around 8:30 PM this evening.

-Timothy Albertson

Hurricane Florence: 2:00 PM Tuesday Update

As of 1:00 PM CDT, Hurricane Florence remains a low end Category 4 Hurricane with sustained winds of 130 mph and gusts up to 160 mph. Florence had weakened slightly overnight, due to an "eyewall replacement cycle" in which she exchanged her old eyewall for a new one. The eyewall of a hurricane is where the strongest winds are located, and usually where the most damage occurs from a hurricane. Eyewalls tend not to cover the entire hurricane, rather they usually extend no more than 40 miles from the center of the hurricane.

During the eyewall replacement cycle, a hurricane may temporarily weaken slightly (sometimes an entire category). During the eyewall replacement cycle, an "outer" eyewall develops and intensifies, and slowly moves inwards towards the "inner" eyewall. This process weakens the inner eyewall, and eventually the outer eyewall takes over.

An area of high pressure over Bermuda is causing Florence to move in a west-northwest fashion; strong hurricanes like to turn right, but the high pressure is preventing her from doing so. This places her on course for a landfall on North Carolina. But will she be a Category 4 Hurricane at landfall?

Recent atmospheric conditions suggest that it is possible that Florence may end up being a Category 3 Hurricane at landfall. She is going to slow down as she approaches land, due to a high pressure moving over the Great Lakes. As mentioned in the previous article; an area of low pressure cannot move an area of high pressure (the high pressure always wins it comes to picking a location). This means that Florence is going to slow down rapidly as she approaches land on Thursday Night, and this could add some shearing which may (as well as other atmospheric details that I spare you details of) start to weaken Florence.

If you remember from a previous article I wrote yesterday about the wind fields of a weakening hurricane, this weakening may mean that Florence's wind field will expand outwards a bit more as she nears land (although the strongest winds will not be as strong as they were before the hurricane weakened).

Her time of arrival on Friday will play a notable role in her exact intensity at landfall. Hurricane Florence is expected to make landfall as a high-end Category 3 or low-end Category 4 Hurricane on Friday Morning. If she is able to advance quicker (and make a landfall on Thursday Night, she will be stronger than if she makes a landfall late, say on early Friday Afternoon).

In addition, her slow movement may mean that she will not make a landfall until possibly Friday, despite being very close to land for most of the day on Thursday. This means that heavy rain falls will be present in eastern North Carolina for a while, and rainfall amounts will be in the inches for several spots across the eastern portion of North Carolina.

Tornadoes are also another hazard when it comes to landfalling hurricanes. Due to the low level shearing present with a hurricane, the outer rain bands tend to rotate and, especially with stronger hurricanes, can produce tornadoes. This is not an uncommon event with a landfalling hurricane (perhaps you remember Hurricane Harvey's tornadoes last year, or the record setting number of tornadoes from a hurricane by Hurricane Ivan in 2004).

Hurricane Watches are in effect for most of the coast of South Carolina and North Carolina. 

-Timothy Albertson

Local Impact From Hurricane Florence

While Hurricane Florence is churning out in the Atlantic Ocean, it will still have an impact on our weather locally. High pressure is dominating the forecast providing sunny skies and temperatures into the low and mid 80s throughout the week. The ridge of high pressure will help to block any potential rainfall from Florence. Both Florence and the ridge of high pressure will help to delay an approaching cold front. The cold front will dip down into the area Tuesday bringing the return of rain into the forecast.

The bigger story is that the cold front will also bring cooler air behind it. We'll see temperatures falling down into the 60s behind the cold front, but that's actually where we should be for this time of the year. Our average highs to end off September and start October are in the mid and upper 60s.