1:25 PM | Tropical activity in the eastern Atlantic

[Latest visible satellite image of the tropical Atlantic Ocean; courtesy Penn State e-wall]

Discussion

All in all, the tropical season so far has been rather quiet in the Atlantic Basin given the frequency of wind shear over the Atlantic Ocean and the steady westward push of dry (Saharan-layer) air off of the west coast of Africa. There is now another tropical wave moving westward in the eastern Atlantic and it should develop into the second named system (Bertha) of the season later this week, but it will face some obstacles in its development in the near term.

[Tuesday analysis of the Saharan Air Layer (SAL) using data from the Meteosat-9 satellite; courtesy University of Wisconsin - CIMSS]

First, this new wave will fight against some rather high wind shear in its vicinity later today and tonight. Varying wind speeds and directions with altitude (i.e., wind shear) is usually an inhibiting factor when it comes to the development of tropical systems. Second, as has been the case quite often this tropical season so far (and last year as well), dry air is pushing westward from western Africa and this wave has to endure more of this Saharan-layer dry air over the next couple of days (yellows, oranges; map courtesy University of Wisconsin - CIMSS). If it should survive the wind shear and dry air - and odds are better than 50/50 - then this tropical wave would likely continue on a west-to-northwest path for the next few days and reach the Antilles Islands region of the eastern Caribbean Sea by the weekend and then the Bahama Islands region by early next week. A second tropical wave follows close behind currently churning westward just off the west coast of Africa, but it is way too early to tell if that system will ever strengthen into a named storm.

2:30 PM | Atlantic Ocean now showing some life

Discussion

The only named tropical system so far this season has been Arthur which formed off the southeast US coastline earlier this month and reached hurricane status (category 2). There is now a pretty healthy-looking tropical wave way out in the Atlantic Ocean and this could eventually become the first “Atlantic-type” tropical storm of the season, but it does have some dry air to penetrate in the near term.

The latest Saharan air layer tracking product (courtesy University of Wisconsin – CIMSS/NOAA-HRD) shows a large expanse of dry air off the west coast of Africa (“oranges and yellows”) that extends well out into the Atlantic Ocean and “in front” of the generally westward-moving new tropical disturbance. This tropical system will encounter some of this African dry air mass in the near term, but it also will be moving into a region with favorable sea surface temperatures of greater 80 degrees. Should the tropical wave survive its encounter with the dry air and develop into a named tropical storm, it would become known as Bertha. We’ll monitor its progress over the next few days here at thesiweather.com.

10:45 AM | The sun has gone quiet...solar cycle 24 continues to rank as one of the weakest cycles more than a century

Discussion

Overview

Ten days ago, the sun was quite active and peppered with several large spots. Now the sun has gone quiet and it is nearly completely blank. The sun goes through a natural solar cycle approximately every 11 years. The cycle is marked by the increase and decrease of sunspots which are visible dark regions on the sun’s surface and cooler than surroundings. The greatest number of sunspots in any given solar cycle is designated as the “solar maximum" and the lowest number is referred to as the “solar minimum” phase.  It appears that the solar maximum phase for solar cycle 24 may have been reached and it is not very impressive. It looks as if this solar cycle is “double-peaked” (see below) which is not all that uncommon; however, it is somewhat rare that the second peak in sunspot number during the solar max phase is larger than the first. In fact, this solar cycle continues to rank among the weakest on record which continues the recent trend for increasingly weaker cycles. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906. Going back to 1755, there have been only a few solar cycles in the previous 23 that have had a lower number of sunspots during its maximum phase. For this reason, many solar researchers are calling this current solar maximum a “mini-max”. Solar cycle 24 began after an unusually deep solar minimum that lasted from 2007 to 2009. In fact, in 2008 and 2009, there were almost no sunspots, a very unusual situation during a solar minimum phase that had not happened for almost a century.

Consequences of a weak solar cycle

First, the weak solar cycle has resulted in rather benign “space weather” in recent times with generally weaker-than-normal geomagnetic storms. By all Earth-based measures of geomagnetic and geoeffective solar activity, this cycle has been extremely quiet. However, there is some evidence that most large events such as strong solar flares and significant geomagnetic storms tend to occur in the declining phase of the solar cycle. In other words, there is still a chance for significant solar activity in the months and years ahead.

Second, it is pretty well understood that solar activity has a direct impact on temperatures at very high altitudes in a part of the Earth’s atmosphere called the thermosphere. This is the biggest layer of the Earth’s atmosphere which lies directly above the mesosphere and below the exosphere. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation and are highly dependent on solar activity.

Finally, if history is a guide, it is safe to say that weak solar activity for a very prolonged period of time (several decades) can have a negative impact on global temperatures in the troposphere which is the bottom-most layer of Earth’s atmosphere - and where we all live. There have been two notable historical periods with decades-long episodes of low solar activity. The first period is known as the “Maunder Minimum”, named after the solar astronomer Edward Maunder, and it lasted from around 1645 to 1715. The second one is referred to as the “Dalton Minimum”, named for the English meteorologist John Dalton, and it lasted from about 1790 to 1830. Both of these historical periods coincided with below-normal global temperatures in an era now referred to by many as the “Little Ice Age”. In addition, research studies in just the past couple of decades have found a complicated relationship between solar activity, cosmic rays, and clouds on Earth. This research suggests that in times of low solar activity where solar winds are typically weak; more cosmic rays reach the Earth’s atmosphere which, in turn, has been found to lead to an increase in certain types of clouds that can act to cool the Earth.

Outlook

The increasingly likely outcome for an historically weak solar cycle continues the recent downward trend in sunspot cycle strength that began over twenty years ago during solar cycle 22. If this trend continues for the next few cycles, then there would likely be more talk of another “grand minimum” for the sun. Some solar scientists are already predicting that the next solar cycle, #25, will be even weaker than this current one. However, it is just too early for high confidence in these predictions since some solar scientists believe that the best predictor of future solar cycle strength involves activity at the sun’s poles during a solar minimum and the next solar minimum is still likely several years away.

Video

httpv://youtu.be/3aRIW4SWkFU

12:15 PM | Kind of a "polar vortex" look to next week's weather maps

[12Z Euro 500 mb height anomaly forecast map for next Tuesday, July 15th; map courtesy Weather Bell Analytics at weatherbell.com]

Discussion

Last summer, the hottest weather in the Mid-Atlantic region took place in the week between July 14th and July 20th with Philadelphia, for example, averaging an impressive 95 degrees for high temperatures over the 7-day period. The same time period this summer - which happens to be next week - looks like it may have a far different result and the upper level weather maps may actually resemble the “polar vortex” pattern made famous this past winter.

Today's European computer forecast model indicates there will be an anomalously strong upper level low situated over the central Great Lakes in much the same manner that occurred frequently during the past winter (see above; 12Z Euro forecast map courtesy Weather Bell Analytics at weatherbell.com). Also, in much the same manner as this past winter, the coldest air relative-to-normal is likely to occur over the Great Lakes and Upper Midwest, but cooler-than-normal air is likely to extend all the way to the Mid-Atlantic coastline. Normal high temperatures have now climbed to 87 degrees in Philly, 89 in DC, and 84 at Central Park, NY and these levels are more than likely not going to be reached for at least a portion of next week. The cold front that will usher in this cool air mass is likely to arrive in the Mid-Atlantic region in the Monday/Monday night time frame - perhaps associated with numerous showers and thunderstorms.

12:30 PM | Arthur caused a dramatic drop in ocean temperatures

[Sea surface temperature (SST) Anomalies before Arthur]

[Sea surface temperature (SST) Anomalies after Arthur]

Discussion

In their very essence, tropical storms are “heat machines” that are fueled by warm sea surface temperatures and they are one of mother nature’s most efficient methods of transporting heat from the tropics to the mid and high latitudes in her ceaseless attempt at balancing out the atmosphere. Often, there can be an immediate impact in this perpetual balancing act of nature with respect to sea surface temperatures in areas near the path of a tropical storm. In fact, Hurricane Arthur, which moved on Friday from the Outer Banks of North Carolina to off the Mid-Atlantic coastline, generated a dramatic drop in sea surface temperatures at the Jersey Shore. As the tropical storm moved over nearby ocean waters, it acted to churn up the water at the Jersey Shore so that colder water from lower levels in the ocean rose to the surface in a process caused “upwelling”. In the same manner that warm air rises and cold air sinks in the atmosphere, cold water will typically sink to lower levels in the ocean as it is more dense than warm water. The “upwelling” generated by Arthur helped to cause sea surface temperatures to plunge at the Jersey Shore from the lower 70’s on Thursday to the upper 50’s on Friday – they have since recovered some back to the lower 60’s. In fact, sea surface temperatures dropped significantly from “pre-to-post Arthur” off the southeast US coastline where Arthur first formed and hovered for a few days (see “before and after” SST maps above). While the change in sea surface temperatures is usually just a short-term phenomenon on the order of days and not weeks, it can act to suppress any new tropical activity until sea surface temperatures climb back to warmer-than-normal levels.

2:00 PM | Possible signs for another snowy winter

["Centrally-based" El Nino during the winters of 2002-2003 and 2009-2010]

Discussion

Winter is still a long ways away, but there are already some developments around the world that can give us a clue as to what kind of weather we can expect here in the Northeast U.S. during the upcoming winter of 2014-2015. One such development is now underway in the tropical Pacific Ocean as El Nino conditions (i.e., warmer-than-normal sea surface temperatures) are gradually forming just off the west coast of South America. There are two important factors with respect to an El Nino – magnitude and location - that can play significant roles in winter weather conditions here in the Northeast U.S.

[CFS model forecast for a "centrally-based" El Nino during the upcoming winter season]

A super strong El Nino would tend to lead to a warm winter in much of the U.S., but I do not expect that to happen despite some model forecasts to the contrary (for more on this: http://thesiweather.com/2014/04/22/1100-am-el-nino-on-the-way-but-odds-are-against-a-super-one/). Meanwhile, a weak-to-moderate El Nino in the tropical Pacific Ocean has been associated with cold and snowy conditions in the Northeast U.S., but it tends to depend on the given location of the particular El Nino. Specifically, weak-to-moderate El Nino’s that are “centrally-based” in the central Pacific Ocean as compared with the warmest sea surface temperatures relative-to-normal being right near the west coast of South America (i.e., “eastern-based") have historically led to snowy winters in the Northeast U.S. For instance, the winters of 2002-2003 and 2009-2010 featured “centrally-based” El Nino conditions and both winters were very snowy in the Northeast U.S. Indeed, there are some longer-range computer forecast models suggesting that this El Nino ultimately becomes “centrally-based” in the Pacific Ocean by the fall and continuing into the winter season. In fact, the similarities between the forecasted sea surface temperature anomalies for the upcoming winter (middle map) and the actual anomalies during the snowy winters of 2002-2003 and 2009-2010 (top map) are rather amazing. Not only are they both featuring "centrally-based" El Ninos in the Pacific Ocean, but both have a noticeable warm sea surface temperature anomaly tucked in near the Alaska coastline and a colder-than-normal region just to its southwest.

We’ll continue to monitor both the magnitude and location of the unfolding El Nino in the Pacific Ocean over the next few months here at thesiweather.com. Currently, it can be said that there are signs that point to a “centrally-based”, weak-to-moderate strength El Nino which could very well result in another snow-filled winter around here.

Video

httpv://youtu.be/Z7qmkpIovHA

1:00 PM | The Atlantic Basin hurricane season has now officially begun and there is an impressive and very fortunate on-going streak

Discussion

The Atlantic Basin hurricane season officially started yesterday, June 1st, and there are actually some signs of tropical activity over the Gulf of Mexico region beginning as early as late this week. The U.S. has been extremely fortunate in recent years to not have a single major hurricane strike (i.e. category 3, 4 or 5). In fact, the last major hurricane to hit the U.S. occurred in October 2005 when Wilma hit southwest Florida as a category 3 storm in that very active tropical season. There have been category 1 and 2 hurricane strikes in the U.S. in recent years including Humberto (Texas), Ike (Texas), Gustav (Louisiana), Dolly (Texas), Irene (North Carolina) and Isaac (Louisiana), but none of those reached the status of 3, 4 or 5 after landfall. [Sandy was not technically a hurricane at its New Jersey landfall (post-tropical cyclone) and, if it were, it would have been categorized as a 1].

Such a streak, or “drought”, in U.S. major hurricane strikes is unprecedented going back to 1900. As of the start of this hurricane season, the span will be 3,142 days since the last U.S. major hurricane landfall. The previous longest span is about 2½ years shorter! During an average tropical season in the Atlantic Basin (using 1981-2010 as a baseline), there are 12 named storms and, of those, 6-7 become hurricanes, and 2 become major hurricanes (category 3-5). By the way, just as a point of comparison, in 1954 the U.S. was hit by 3 major hurricanes in less than 10 weeks.

For more on the 2014 Tropical Outlook: http://thesiweather.com/2014-tropical-and-mid-atlantic-summer-outlooks/

Days between major hurricane landfalls in the U.S., 1900-2013. (Credit: Roger Pielke, Jr., University of Colorado)

12:00 PM | Solar cycle 24 continues to rank as one of the weakest on record; the "solar maximum" phase of solar cycle 24 may have been reached and it is not impressive

[Current solar image with very few sunspots]

Discussion

Overview It appears that the solar maximum phase for solar cycle 24 may have been reached and it is not very impressive. In fact, this solar cycle continues to rank among the weakest on record which continues the recent trend for increasingly weaker cycles. Going back to 1755, there have been only a few solar cycles in the previous 23 that have had a lower number of sunspots during its “maximum” phase (plot below; courtesy Doug Biesecker of NOAA/SWPC). For this reason, many solar researchers are calling this current solar maximum a “mini-max”. Solar cycle 24 began after an unusually deep solar minimum that lasted from 2007 to 2009. In fact, in 2008 and 2009, there were almost no sunspots, a very unusual situation that had not happened for almost a century.

["Red line" represents solar cycle 24 showing far fewer sunspots during its maximum phase compared to most cycles going back to 1755]

Consequences of a weak solar cycle First, the weak solar cycle has resulted in rather benign “space weather” in recent times with generally weaker-than-normal geomagnetic storms. By all Earth-based measures of geomagnetic and geoeffective solar activity, this cycle has been extremely quiet. However, there is some evidence that most large events such as strong solar flares and significant geomagnetic storms tend to occur in the declining phase of the solar cycle. In other words, there is still a chance for significant solar activity in the months and years ahead.

Second, it is pretty well understood that solar activity has a direct impact on temperatures at very high altitudes in a part of the Earth’s atmosphere called the thermosphere. This is the biggest layer of the Earth’s atmosphere which lies directly above the mesosphere and below the exosphere. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation and are highly dependent on solar activity.

Finally, if history is a guide, it is safe to say that weak solar activity for a prolonged period of time can have a negative impact on global temperatures in the troposphere which is the bottom-most layer of Earth’s atmosphere - and where we all live. There have been two notable historical periods with decades-long episodes of low solar activity. The first period is known as the “Maunder Minimum”, named after the solar astronomer Edward Maunder, and it lasted from around 1645 to 1715. The second one is referred to as the “Dalton Minimum”, named for the English meteorologist John Dalton, and it lasted from about 1790 to 1830. Both of these historical periods coincided with below-normal global temperatures in an era now referred to by many as the “Little Ice Age”. In addition, research studies in just the past couple of decades have found a complicated relationship between solar activity, cosmic rays, and clouds on Earth. This research suggests that in times of low solar activity where solar winds are typically weak; more cosmic rays reach the Earth’s atmosphere which, in turn, has been found to lead to an increase in certain types of clouds that can act to cool the Earth.

Outlook The increasingly likely outcome for an historically weak solar cycle continues the recent downward trend in sunspot cycle strength that began over twenty years ago during solar cycle 22. If this trend continues for the next couple of cycles, then there would likely be more talk of another “grand minimum” for the sun. Some solar scientists are already predicting that the next solar cycle, #25, will be even weaker than this current one. However, it is just too early for high confidence in these predictions since some solar scientists believe that the best predictor of future solar cycle strength involves activity at the sun’s poles during a solar minimum and the next solar minimum is still likely several years away.

Video

httpv://youtu.be/K98k1NaN__c

1:00 PM | First signs of potential tropical activity in the Atlantic Basin

[Latest European model forecast of MJO index; "green line" represents the model forecasted daily movement of the MJO index through phases 2 and 3 during the period from May 29th to June 12th]

Discussion

The official start to the Atlantic Basin hurricane season is this Sunday, June 1st, and there are some signs that there could be some early tropical activity to monitor. The Madden-Julian Oscillation (MJO) index is raising the possibility of tropical troubles in the Atlantic Basin during the early-to-middle part of June and this could ultimately have an impact on the east coast. The MJO index tracks a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days. The MJO has wide ranging impacts on the patterns of tropical and extratropical precipitation, atmospheric circulation, and surface temperatures around the global tropics and subtropics. Research has found that the location or “phase” of the MJO is linked with certain temperature and precipitation patterns around the world. The very latest MJO forecast by the European computer forecast model (see plot above) propagates the MJO index into phases 2 and 3 during the early-to-middle part of June and studies have shown that these two phases tend to be correlated with increased tropical activity in the Atlantic Basin.

Indeed, the last few GFS computer forecast model runs have been hinting at some possible development late next week in the western Caribbean Sea or southern Gulf of Mexico region (see forecast map below) and this potential tropical disturbance could ride up the eastern seaboard. In fact, the first named tropical system last year, Tropical Storm Andrea, formed during the early part of June in a period in which the MJO index passed through phases 2 and 3. That system developed near the Yucatan Peninsula region of Mexico, tracked across northern Florida, and then moved right up the eastern seaboard producing more than three and a half inches of rain in Philly on June 7th and 8th.

[GFS computer model forecast from yesterday for late next week showing a disturbance in the southwestern Gulf of Mexico with plenty of moisture; forecast map courtesy Weather Bell Analytics at weatherbell.com]

11:15 AM | Amazing cloud formation in supercell thunderstorm

Discussion

A supercell is defined as a thunderstorm that is characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. One such supercell thunderstorm in northeast Wyoming on Sunday produced some spectacular cloud formations and little in the way of precipitation which is a key in the great viewing. These “low precipitation” supercells are more common in the Plains or northern Rockies where dry air often interacts more easily during their formation as compared to locations on the east side of the Mississippi River. In fact, due to the little rainfall produced from this type of “low precipitation” supercell, the storm’s rotation is viewed more easily. Normally, precipitation obstructs the view of the cloud structure that develops with the normal supercell rotation. A two-minute video (below) of the developing supercell is available on YouTube (picture and video courtesy of the storm chasers team called “Basehunters Chasers”).

Video

httpv://www.youtube.com/watch?v=VoO89cqDgJU