Text Forecast for Invest 98 - July 22, 2013

Invest 98 is currently exiting western Africa as a vigorous tropical wave. This is my current prediction for its track, strength and any other additional variables.

Track
Invest 98 is expected to move generally west-northwest as the atmospheric flow for this wave will allow it to progress in that general direction. An intense area of westward winds is observed in the Caribbean, which may hinder projections of a west-northwestward motion. However, the current model consensus is for the WNW track to verify. The top analog tracks for previous tropical cyclones in the immediate vicinity of Invest 98 show a decisive out to sea solution for this system, where it would move northwest and curve around in the Atlantic in the direction of Europe. Ensemble forecasts agree with this proposal.

Intensity
The lack of entry into the Caribbean indicates this invest will most likely stay below hurricane strength. While I indicated this strength level was possible a few days ago, more recent model forecasts have eliminated that idea. Tropical storm status is certainly attainable for this invest, although the length of time the invest is able to hold the TS title is very much in question.

Landfall potential
The potential of a landfall on the US mainland is low. Any threat of a landfall is greatest in the Mid-Atlantic, which may feel some of the invest's effects as it curves out to sea.

Andrew

Strong African Tropical Wave Could Develop Into a Hurricane

A strong tropical wave currently over far western Africa has potential to develop into a tropical cyclone in the open Atlantic basin before possibly attaining hurricane status closer to the Caribbean.

Infrared satellite imagery indicates the presence of a vigorous tropical wave over western Africa. Short range GFS model products indicate this tropical wave will push off into the open Atlantic in the next 72-84 hours, before the first signs of development appear. It appears the system fluctuates in strength after development into a rather weak tropical cyclone takes place in the next week or so.

Pushing ahead into the 10-14 day mark, model forecasts develop the tropical system into a stronger tropical storm or a weak hurricane as the cyclone approaches the Caribbean. Previous forecasts from the GFS model take the system anywhere from scraping the Eastern Seaboard to an entrance into the Gulf of Mexico. Based on climatological tracks from where the tropical wave is now, and the current atmospheric flow for tropical waves and/or tropical systems above the 1000 millibar mark, I find the track towards the Gulf of Mexico more likely. A certain caveat is the potential that the atmospheric flow changes drastically, in which case a different track may be favored. But at this point in time, I am hard-pressed to find another track I find more favorable than at least an entry into the eastern Caribbean.

Andrew

Text Forecast for August, 2013

This is a text forecast for the month of August, 2013.

After a heat wave across much of the nation in the middle of the month, it is expected that the month of July will be seen as the more intense month when compared to August.

I anticipate the atmosphere to favor high pressure formation across the West Coast into the Rockies, as a rather strong negative correlation exists between June values of the Antarctic Oscillation (AAO), and mid level height anomalies across the Rockies and the West Coast, and even towards New England and the waters off that area. The AAO ended up negative for the month of June, thus my expectation of high pressure formation across the Rockies.

I do expect periodic instances where the high pressure system in the Rockies will propagate into the Plains and possibly eastward into the Ohio Valley. This probability would rise if the New England area also experiences high pressure growth due to the aforementioned negative correlation. 

The Midwest and portions of the Plains will likely endure multiple cool weather periods, as disturbances drop in from Canada and set up a depression in the jet stream that will offer rather enjoyable temperatures in these regions. The passage of cold fronts through these areas also increases the chance of precipitation across the middle of the nation, so it is not a bad idea to believe these areas have a shot at above average precipitation for the month of August.

Primary severe weather event location is expected to stretch from the Northern Plains to the Midwest, as disturbances riding the jet stream will couple with intermittent cold front passages in the Midwest to highlight these areas for severe weather potential. Tornado numbers are expected to end up below average for the month of August, due to a lack of a highly meridional (very wavy) jet stream and displacement of the highest instability to the south of the main upper level flow. Any tornadoes that do occur would be favored in the Northern Plains, at the peak of the jet stream above the high pressure system in the Rockies.

-Forecast Summary by Region-

Midwest

Precipitation: Above Average

Temperature: Slightly Below Average

Northeast

Precipitation: Slightly Below Average

Temperature: Slightly Above Average

Southeast

Precipitation: Below Average

Temperature: Average

South Central

Precipitation: Average

Temperature: Average

West

Precipitation: Above in north, Below in south

Temperature: Average to Above Average

Andrew

Long Term Effects of Coldest Arctic Temperatures Since 1958

Yesterday, I posted about how the Arctic was experiencing the coldest temperatures for this time period since before 1958, as the image below shows. Now that we've clarified the presence of an anomalous cold trend in the Arctic, what could this mean for long term effects into the fall and early winter?

I discussed yesterday how a main effect of these below normal temperatures will be the hampering of Arctic sea ice melt. This means the sea ice extent is most likely going to stay well above the record-breaking low ice we saw last year. What it also means is an increased chance of low pressure formation in and around Greenland, known by many as the positive phase of the North Atlantic Oscillation.

In a study I recently uncovered, it has been detailed that above normal temperatures in the Arctic help lead to exaggerated sea ice. It is this exaggerated loss of sea ice that then leads to the tendency for the negative phase of the North Atlantic Oscillation to develop. The negative NAO involves high pressure formation in or around Greenland that then positions itself over that land mass for a prolonged period of time. In response to the negative NAO, colder air (and rising snow chances in winter) is encouraged to enter the Northeast and East US.

If we begin to see low pressure start to form more often around Greenland entering fall, I would not be surprised to see that the cause of it is this colder than normal Arctic environment. This may pave the way for a fall with generally warmer temperatures and not such a variable flow that would allow for big temperature swings.

It is worth noting that these below normal temperatures appear to be centered in or around the area where these Arctic temperatures are taken. Reanalysis of the month of June shows very slight below normal temperatures across the North Pole, but rather significant above normal temperature anomalies across Northern Canada into the Bering Sea. This will be an interesting factor to watch how the sea ice in those areas responds to the above normal temperatures in June that may continue through this month.

Andrew

Arctic Temperatures Coldest Since 1958

Temperatures being observed at the Arctic are the coldest observed at this time period since at least 1958, leading to additional speculation that this winter could be different than those observed in the past while.

The chart above shows latest temperatures in the Arctic over 2013. The winter is shown at the left of the chart, where you can see the wild fluctuations in temperatures as the stratospheric warmings we discussed in depth last winter aided high pressure development that eventually led to warmer than normal temperatures. However, now that we are in the summertime, the Arctic has calmed down for the season. These unusually cool temperatures can easily be used for those interested in the global warming debate, but I'm not here to discuss that right now.

Arctic sea ice melt is likely to be hampered. Below normal Arctic temperatures, while still above freezing, set the stage for a probable lessening of the severity of ice melt anticipated this summer. While we still expect to fall well below average sea ice levels, it is very possible that this season's sea ice extent will be unlike last year, where we hit a record low in sea ice, but more like sea ice levels roughly a decade ago.

It is likely we will find more correlations between this temperature anomaly and other atmospheric factors later on in the year, but for now, it is something to keep an eye on.

I will have an add-on piece to this article tomorrow.

Andrew