Jan 14, 2016

A hui hou to Pali

While Atlantic Hurricane Alex has formed this morning over the Northeast Atlantic, former Central Pacific Hurricane Pali is in a rapid weakening phase.

Pali initially formed on 31 December 2015, as a tropical depression about 1850 miles to the SW of Honolulu. Pali moved toward the NW and on the evening of January 7th (Local Hawaii time) became a tropical storm with winds of 45 mph while located about 800 miles SW of Honolulu. Thereafter Pali took a meandering slow track toward the west and then southwest and south southeast over the following 4 days. Gradually the TS organized and intensified into a Hurricane by late afternoon on the 11th.

Pali remained  hurricane and intensified to a Category 2 hurricane on the 12th. Thru the 13th Pali continue to meander SOUTH towards the equator. Its position was now within 3 degrees latitude north of the equator! Late on the 13th the combination of decreasing latitude (Pali was nearing the equator) and strong SW wind shear aloft cause a rapid weakening of the storm.

Today Pali is now a tropical depression near 2.5°N and 173.0°W. Pali is rapidly weakening and forecast to dissipate during the next 24 hours.

Here is a link    The Life of Hurricane Pali  to a movie on my YouTube channel of Pali's track from inception to its current demise.

From Byers and Riehl, Tropical cyclone characteristics are as follows:
  1.  they have a greater chance to farm during the summer and fall seasons in either hemisphere.
  2. they form over the warmer waters of subtropical and tropical ocean basins, (Usually with ocean temperatures of 26°C or >)
  3. they have no warm or cold fronts associated with them.
  4. pressure and other properties (winds, rain) tend to be distributed symmetrically
  5. they are seldom observed within 5­° of latitude of the equator, This is because the Coriolis force is important in their development.

    What is the Coriolis force? It is an artifact of the earth's rotation. Basically "things" in motion on the surface of the earth experience a deflection of their motion due to the earth's rotation. In the Northern Hemisphere this deflection is to the right of the object's apparent motion. (In the Southern Hemisphere the deflection is to the left.) For a very good and brief explanation on Coriolis check out this link: What is the Coriolis Force ?

What do you know? Alex is a Hurricane !

Morning satellite pictures (Fig. 1) indicate that Alex has intensified and developed an eye and has now been classified as a hurricane in the far northeast Atlantic Ocean.

(Fig 1.) Visible satellite imagery of hurricane Alex

The Azores Meteorological Service has issued a Hurricane Warning for the islands of Faial, Pico, Sao Jorge, Graciosa, and Terceira in the central Azores, and a Tropical Storm Warning for the islands of Sao Miguel and Santa Maria in the eastern Azores.

Alex is forecast to move across the Central Azores with increasing winds expected to begin to affect the islands by late tonight. Here is the past track and forecast track for Alex is shown below in Fig. 2

(Fig. 2) Alex ' past and forecast track
After passing north of the Azore on Friday Alex is forecast to curl towrad the NNW or NW and merge with a large extratropical low south of Greenland over the weekend.

According to the NHC Alex is the first hurricane to form in the month of January since 1938, and the first hurricane to occur in this month since Alice of 1955.

Jan 13, 2016

Out of Season Subtropical Storm in the Atlantic

The Atlantic Ocean has its first named (sub)tropical cyclone of the year. Alex has formed over the far eastern subtropical waters of the Atlantic Ocean. Last week on the 7th of January the National Hurricane Center (NHC) issued a special Tropical Weather Outlook (TWO), highlighting that an intense extratropical storm could acquire subtropical or tropical features within a week or so as it moved over the warmer waters of the subtropical eastern Atlantic, Ocean.
NHC TWO from Jan 7 2016

Quick Discourse on extratropical, tropical and subtropical lows

EXTRATROPICAL (XT) LOWS develop when potential energy is released due to warm and cold air masses interacting with each other. (Meteorologists call this baroclinicity). XT lows have fronts within their circulation (cold fronts/warm fronts). Winds can be light or very strong. In the more intense XT lows winds can be at or above hurricane force. In addition, the pattern of wind and precipitation with respect to the center of the low can be asymmetrical, that is not necessarily concentrated near the center of the storm. Lastly the core of the storm, especially aloft, exhibits cold temperatures. XT lows can form over land or over the ocean. They also tend to form in mid or high latitudes.

TROPICAL CYCLONES (TC) form over warm ocean waters with a water temperature of 25C-26C or higher. They develop over the subtropical and tropical oceans of the world mostly during the summer and fall months.Tropical cyclones are warm core systems. The energy that allows them to intensify is the latent heat that is released when moisture in the air condenses.  TCs have NO frontal features. Temperatures warm steadily as one gets to the center of the TC. Wind and precipitation tend to be symmetrical with respect to the storm; the most intense rain and wind are near the center. (If the TC becomes a hurricane then center or EYE is often dominated by light or even calm winds and minimal cloud cover and rain).

SUBTROPICAL CYCLONES (STC) are more or less hybrid systems. They often form in one of two ways. One is when an upper air storm with cold air aloft moves over warm SSTs. Cold air over warmth is unstable and thus thunderstorms and cloud formation increases.These type of ST lows tend to be rather large in circulation with a broad area of light winds and cloudy skies in the center. The strongest winds tend to be well removed from the center along with the more intense precipitation.

The second way a ST low can form is when an XT low moves over warm SSTs  (in this case as cool as 19C-24C).  and thunderstorms increase near the center of the low. The system then "warms" and begins to lose its frontal features. These types of ST lows tend to be relatively small in size.usually no more than 300 miles in diameter and some have had diameters as small as 100 miles across (midget cyclones).

If an STC moves over SSTs of 25-26C or greater it can develop a warm core and in turn  become completely warm core or tropical.

About Subtropical Storm Alex

Our newest subtropical storm (STS) Alex has evolved and developed from the latter scenario. On January 6 and 7 2016 and intense XT storm developed between the Bahamas and Bermuda. For the next 5 days it tracked east-northeast across the central subtropical Atlantic Ocean.
Track of Low that became Subtropical Storm Alex

 In time it began to move over marginal warm SSTs and started to lose its XT features and fronts. The SST map below from Environment Canada shows the water temperatures along the track of the low and the current location of  STS Alex. SSTs are 22-24C along and beneath the storm.

Sea Surface Temperatures across the North Atlantic and in the vicinity of STS Alex
STS Alex is forecast to gradually turn NE then N-NNW over the next few days. It will be moving over colder water temperatures so transitioning to warm core or tropical is not expected.

Official NHC track for STS Alex
 However, a surge of very cold air over Eastern North America will move out across the Atlantic and interact with Alex. Once again baroclinic elements will come together and Alex will once again intensify as rejuvenated extratropical storm impacting the shipping lanes of the North Atlantic.

Below is an infrared satellite of Alex over the Eastern Atlantic. Sat pic from Environment Canada
Satellite picture of STS Alex
From the NHC's forecast storm discussion from 5 PM AST 13 Jan: Alex is the first tropical or subtropical storm to form in January since an unnamed system did so in 1978, and is only the fourth known to form in thismonth in the historical record that begins in 1851.

Fascinating! Tomorrow I'll talk more about Alex and on Hurricane Pali in the Central Pacific, far far to the southwest of Hawaii, As a matter of fact Pali is closer to the equator than it is to Hawaii.

Jan 10, 2016

January 10, 2016 Mild, Wet and Wild Weather Day....

Wild weather day up here across Upstate New York :

  Record warmth: High of 55° Albany and 65° in Poughkeepsie both record high temperatures for this date

Selected high temperatures for Jan 10th 2016

There was a rapidly NNE moving squall line between 1-4 PM that impacted eastern NY State and Western New England  with thunderstorms producing wind gusts of  35-50 mph in places and some small hail too

Also had a plethora of rainbow reports and pictures, too. Here are 3 of the many pictures
Tom Cowin/Troy, NY

Gwen Ivins/Location Unknown

David Wood/Troy, NY

By morning we'll be be 20-25 across most of the region. Lake effect snow showers already over the NW portions of the Adirondacks and they'll be spreading east and south through the night and Monday. Hope you enjoyed today's very brief January thaw!