Sep 5, 2013

Hug your Honey Weather Tonight

We are forecasting the season's first frost and/or freeze for some area for this overnight and early Friday morning. In general this "first" frost is a bit ahead of the average dates for a first frost. Here is a map of the average times for first frosts for NY State from Cornell University

For the Adirondacks of NY tonight's expected frost is fairly close to normal time of occurrence but for other locations that are under a frost advisory its about 10 days to 2 weeks sooner. Here is where freeze and frost warnings are posted for the NEWS10 viewing area:

Here are some of the low temperatures that we are forecasting for tonight for the Adirondacks, Mohawk Valley, Upper Hudson Valley and Vermont. By the way, the record low for September 6th for Glens Falls is 34° set in 2000, so there could be some record lows for that location

For the rest of the viewing area here are tonight's expected lows
The record low for Albany is 38° set in 1938 so we could take a run at this record if we calm out quickly over night. Below are the average dates for the first frost for a few select locations, including the earliest and latest dates for the occurrence of  the first frost. (Thanks to my colleague Steve Caporizzo for the images and data).

For the Adirondacks and Glens Falls the chances to get a first frost of fall before Sept 10th-14th period is 10% probability of occurrence; so this is indeed a rare occurrence and if it does happen, for some locations it could be the earliest occurrence date ever! Keep in mind that local climates can affect frost formation. For example, if a location is near a body of water then frost formation could be delayed or not happen at all due to the warming effects that that water body exerts locally. Conversely a valley  under the right conditions of no warming effects from a body of water, clear skies, calm winds and cold air drainage (from off the mountains surrounding the valley) can radiate heat efficiently at night and chill down quiet easily.

Now tonight's expected frost and/or freeze will have more of an impact on an individuals garden (like mine where I still have plenty of green tomatoes!) versus impacting fruit orchards like apples. As a matter of fact tonight's cold weather is actually good for the apples and should make for some fine picking very soon!

Quick Update on the Tropics

Activity has increased a bit over the Atlantic basin over the past few days. Here is the Thursday morning Tropical Weather Outlook from the National Hurricane Center:

 Late yesterday a Tropical Depression (#7) formed to the south of Puerto Rico and then briefly intensified into Tropical Storm Gabrielle late yesterday evening. Today the system has once again weakened into a poorly organized depression. The weakening occurred due to proximity to the islands in the Greater Antilles (namely Hispaniola) and strong winds aloft from the west causing shear. As I stated in my previous post on the tropics shear is an unfavorable element for tropical cyclone development.

As I also mentioned in my last blog post with the negative factors currently in place across the Atlantic for the moment only a few geographic locations over the basin favored potential development. One area that I mentioned was the Bay of Campeche. This morning an area of disturbed weather (satellite image to the left)  is showing some increase in organization and convection. There is a bit of shear aloft over the system at the moment but it is forecast to ease during the next 12-24 hours. As this disturbance moves W-WNW over the next 24-36 hours, there is a chance for it to become a tropical depression or a tropical storm before it moves onto the mainland of Mexico.

Lastly there is a 3rd area of showers and storms over the Eastern Atlantic to the west of the Cape Verde Islands. This is associated with a tropical wave. It is poorly organized with no signs of a closed low pressure circulation. Numerous negative factors - shear and SAL ( see my previous blog post to learn more about SAL) over the next few days will preclude any significant development of this system.

So as it stands now the Atlantic has had 7 named tropical systems and still NONE have become  hurricane.

Sep 1, 2013

Let's Hope it stays this way

The peak of the Atlantic hurricane season is approaching, the date is September 10th and so far we have not had ONE hurricane yet in the Atlantic basin. The last time there were no hurricanes in the Atlantic through this point in the season was 2002. Now the quietness of the season thus far is no guarantee that it will remain so thus we should not let our guard down but it is interesting nonetheless.

Why so inactive?

Thus far we have had five named tropical systems all of tropical storm intensity; this number is about normal for the number of named storms for this point in time in a hurricane season. One storm,  Andrea, made landfall on the U.S. mainland bringing beneficial rains to a drought  parched Southeast U.S.

A number of factors have come into play making for an inactive season so far:

First the Bermuda high a large area of high pressure that spans the Atlantic Ocean has averaged out to be a bit stronger than normal thus far this summer. Higher than normal pressure across the Atlantic is an unfavorable factor for tropical cyclone development.. (However I will point out that over the past week or so the overall strength of the high is weakening a bit). Another note about this high is that it is a bit farther south  of its "normal" climatological position,

Second, at times across the tropical latitudes of the central and east-central Atlantic a Tropical Upper Tropspheric Trough or TUTT has persisted; depending on the configuration of the trough, strong SW or W winds aloft have occurred over this part of the Atlantic. Both TUTTS and strong winds (shear) are unfavorable factors for tropical cyclone genesis or intensification.

Third blame it on SAL. SAL or Saharan Air Layer is a cloud of dust or better yet SAND from the Sahara Desert that moves westward off of the continent of Africa and then out over the Atlantic Ocean. There have been at least three occasions this summer where SALs have migrated all the way across the ocean to Texas! SAL and all that it carries with it - the warm, dry (stable) and sandy air are negative factors for tropical cyclone development.

Currently yet another SAL is moving off the west coast of Africa

So far through from June 1st the start of the Atlantic Hurricane Season through August 27 of this year, largely because of the SALs that have moved off of Africa, the average relative humidity over the Atlantic has been way below normal. (Keep in mind tropical cyclones "like" warm and moist air in and around their circulations NOT warm and dry air). Here is a map of the departure from normal of the mean relative humidity (from NOAA):

For more on SAL checkout: What is SAL .   So for at least the next week tropical cyclone activity should remain on the quiet side.

What areas are favorable for tropical storm formation?

Right now little shear and moist air is confined to a relatively small area of the Atlantic basin, namely the Western Caribbean Sea and the extreme south portions of the Gulf of Mexico(Bay of Campeche). If any tropical systems can move or form over these locations over the next few days conditions are "marginally" favorable for some possible development.

Some other interesting points

The least number of storms that has occurred in the Atlantic in any given Hurricane season is 4 (1983).

It has been been 7 years and 10 months since a major (category 3 or greater) hurricane has struck the U.S. This is the longest streak on record. The last time the U.S had a major hurricane make landfall was Wilma in 2005.

Between 1962 and 2012 (50 years) an average of 5.6 major hurricanes per decade made landfall on the U.S. For the preceding 50 years (1911 and 1961) an average of  8.4 major hurricanes struck the U.S.

Global hurricane activity has actually been in decline over the past 40 years (in spite of some active years in the Atlantic:

Let's hope it stays this way! ;-)