The overall numbers are likely to be slightly below-normal this year in terms of the number of tropical storms and hurricanes in the Atlantic Basin (includes the Caribbean Sea and Gulf of Mexico) with around 11 named tropical systems, 5 hurricanes and 2 majors. In a normal Atlantic Basin tropical season, there are about 12 named storms with 6 reaching hurricane status and 3 actually reaching major status (i.e., category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale).
The major factors involved with this year’s tropical outlook include the likely continuation of El Nino in the equatorial Pacific Ocean. In addition, the Atlantic Ocean is sending mixed signals in terms of the prospects for tropical activity this season with some sections featuring (unfavorable) colder-than-normal sea surface temperatures and others featuring (favorable) warmer-than-normal waters. The sea surface temperature pattern in the Caribbean Sea, Gulf of Mexico and western Atlantic Ocean (i.e., warmer-than-normal) makes the southern and eastern US somewhat vulnerable to what I call “home-grown” tropical hits during this upcoming tropical season.
In the long term, the sun is the main driver of all weather and climate and multi-decadal trends in solar activity can have major impacts on oceanic and atmospheric temperatures. In addition, empirical observations have shown that the sun can have important ramifications on weather and climate on shorter time scales including those associated with the average solar cycle of around 11-years. For example, there is evidence that low solar activity during solar minimum years tend to be well-correlated with more frequent “high-latitude blocking” events compared to normal and this type of atmospheric phenomenon can play an important role in the winter season.
Several key factors listed below have been examined for the “2018-2019 Winter Outlook” and they suggest to me that this will be a colder-than-normal and snowier-than-normal winter in much of the eastern and southern US:
1. Weak-to-moderate “centrally-based” El Nino in the tropical Pacific
2. Warmer-than-normal water in the northern Pacific
3. Low solar activity
4. High-latitude blocking
5. Northern Hemisphere snowpack
6. Analog years
7. Soil moisture
The climatological peak of the Atlantic Basin tropical season is around the middle of September and it certainly looks like there will be a ramp up in activity after a relatively quiet month of August. In fact, there very well may be a burst of activity with potentially several named storms over the next 2 or 3 weeks taking us right into the middle of September. Two areas of interest currently exist and the "front-runner" of these two systems could actually have an impact on Florida and the Gulf of Mexico by the early-to-middle part of next week. The second system is still not far off of Africa's west coast and it will have to be closely monitored given the expected strong high pressure ridging next week across the Northeast US and southeastern Canada.
The Pacific Ocean is the planet’s biggest and its sea surface temperature (SST) pattern has a tremendous influence on all weather and climate around the world. In particular, El Nino conditions (warmer-than-normal) in the equatorial part of the Pacific Ocean can have a tremendous impact on winter weather in the US depending on its intensity and duration. In addition to duration and intensity, the specific location of an El Nino in the equatorial Pacific Ocean can be quite crucial to wintertime temperatures and precipitation patterns in the US and current signs point to a weak-to-moderate strength El Nino that is “central-based” and this raises the prospects for a cold and snowy winter in the eastern US.
The Atlantic Basin has been relatively quiet in recent days in terms of tropical activity and it continues to look like this will be a less active tropical season compared to 2017. One of the main factors that led us to an outlook for a less active tropical season back in the springtime was the large patch of colder-than-normal water at that time in the eastern Atlantic Ocean. This continues to exist and is quite likely an inhibiting factor for the formation or intensification of tropical activity in the tropical Atlantic and there are a couple other factors as well that are likely deterring activity. First, Saharan Desert (dry) air has persistently flowed westward from western Africa and into the tropical Atlantic and there are signs that this general pattern will continue into at least the near future. In addition, wind shear has been quite prominent across the tropical Atlantic in recent days and there are reasons to believe that this will continue to impede tropical activity in coming weeks. Don’t let your guard down; however, as all it takes is a direct hit by one storm to make it a memorable tropical season.
The summer solstice has just passed and the days will grow shorter and shorter from here on out until the winter season gets underway. While winter is still a long way off, there are already some clues that can provide some insight as to what kind of weather we can expect around here in the Mid-Atlantic region. First, signs point to the formation of warmer-than-normal sea surface temperatures by the upcoming winter season in two key areas of the Pacific Ocean: 1) the central equatorial region and 2) the Gulf of Alaska. Second, there is little doubt that solar activity will remain on the low side through the upcoming winter season as we are rapidly approaching the next solar minimum phase from an already historically weak solar cycle #24. Finally, one important wintertime cold air source region for the Mid-Atlantic is Greenland and it is currently experiencing above-normal snow and ice cover. While this is in the speculation phase, all of these factors point to the possibility of cold and snowy conditions in the Mid-Atlantic region during the upcoming 2018-2019 winter season.