Day 243: Complicated East Coast Pattern
Many people are focused on Major Hurricane Earl tonight, wondering what the eventual path will be. The official forecast from the National Hurricane Center (NHC) continues to keep Earl just off the east coast of the United States. However, because of the large size of Earl’s wind field, a hurricane watch has been issued for portions of North Carolina. Even if the eye does not make landfall, it should be close enough that portions of North Carolina will experience some wind and rain.
The eventual path of Earth will be dictated by events that are currently well removed from the hurricane. A strong short-wave trough at 500 mb is forecast to race across the northern plains over the next few days. The southeast shear downstream of the trough axis is forecast to help “steer” Earl to the north and northeast. The speed at which the short-wave trough moves across the northern United States will be impacted by the strength of the ridge over the eastern United States (center denoted by a “N” below).
Rotating around the periphery of the east coast ridge are several mid- or upper-level lows (denoted by small letter “x”). Currently, these upper-level lows are resulting in strong shear (by hurricane standards) across the top of Earl. As these upper-level lows continue to move westward, away from Earl, the shear should decrease allowing for possible strengthening. Might these upper-level lows aid the destruction process of the ridge?
I still don’t think it is wise to rule out a potential North Carolina landfall. Even if Earl does not make direct landfall, it will be close enough to cause significant societal impacts. A second area where landfall is possible is in New England, as hurricane Earl races ahead of the vigorous 500mb short-wave trough.
Day 242: Major Hurricane Earl
Hurricane Earl has intensified to a category 4 hurricane today, passing within 100 miles of San Juan, Puerto Rico. As you can see from the radar images, Earl is extremely well organized.
I know the official National Hurricane Center (NHC) forecast (as of this writing) calls for Earl to miss the east coast of the United States, I have seen enough stuff today to leave me with serious concerns with this forecast. All interested on the east coast, from South Carolina to Maine, should monitor Earl’s progress extremely closely. It is far from certain that Earl will not make landfall along the east coast…
Day 241: Cone of Uncertainty: New York City Edition
When viewing National Hurricane Center (NHC) forecast graphics, people tend to focus on the specific location of the icons, or the path between the icons. Taking the forecast at face value, the east coast of the United States has nothing to worry about with Hurricane Earl.
Unfortunately, hurricanes are not simply points in the Atlantic Ocean. They are large, spiraling storms that can span several hundred miles. Even if the eye of the hurricane does not pass directly overhead, dangerous weather might be still affect your area. Also, there is considerably uncertainty with hurricane track and intensity forecasts as the forecast time increases. Thus, forecast track errors can exceed 200 miles 4 and 5 days out. Keeping this uncertainty in mind, several major cities along the east coast need to monitor closely for possible impacts from Hurricane Earl. Both New York City and Boston are within the “Cone of Uncertainty“.
Day 240: Certain Uncertainty and the Role of Humans in the Forecast Process
Several recent posts have discussed tropical cyclones occurring in the Atlantic Ocean. Today we’ll focus on the eastern Pacific Ocean, where Tropical Storm Frank is currently spinning away. This is important because of something I mentioned in last night’s post.
As the large west coast trough continues to develop, the flow on the east side of the trough will be out of the southwest. This means that if Tropical Storm Frank moves far enough northward, it could be absorbed by the large scale western-United States trough. This would bring tropical moisture into the southwestern United States and into the central US, coincident with a frontal boundary. This is a recipe for heavy rain and flooding.
So what is Tropical Storm Frank going to do? Well, I know a lot of non-meteorologists think that all meteorologists do is take the models and give them to the public. Well…
The image above depicts the suite of model forecast guidance available to forecasters regarding the track of Tropical Storm Frank. Based on this model forecast guidance, where is Frank going to go? If you ask me, the only thing certain about the future of Frank is that it is uncertain!
This is why we, as a society, need to have humans involved in the forecast process. If we were to take the average of all of these forecasts (sort of an ensemble consensus approach) we might very well be left with a forecast that doesn’t move Tropical Storm Frank at all. However, if we compare this consensus forecast (stationary) to the individual model forecasts, we see that consensus is not a good representation of the possible outcome. A human can take the forecast track information from the models, apply meteorological principles and theories, and thus improve the model guidance to produce a better forecast.
To all meteorologists, particularly meteorology students, when you take a model forecast and use it at face value you are essentially telling me that you are unnecessary. This is most prevalent in your forecast discussion. I can’t tell you how many times I’ve read National Weather Service forecast discussions that basically tell me what forecast model the human forecaster used for his or her forecast. It is not enough for human forecasters to simply provide the best forecast; human forecasters MUST demonstrate they add value to a model forecast or risk being replaced by the model(s). This added value can range from explaining the uncertainty in the forecast, to communicating the potential impact, or producing a better forecast when the model guidance is significantly in err.
You might not be the best forecaster, but you can always add value to a model forecast. If you do this every time you produce a forecast, you’ll have more job security than someone who doesn’t.
Day 239: Upper-Level Moisture Returning to Central United States
The weather has been quite pleasant the past few mornings/evenings across the central United States. One reason for the cooler weather can be attributed to the dry air in the wake this week’s cold front. Why is this? Water, including water vapor, heats and cools at a slower rate than dry air. This means dry air heats up during the day faster than moist air, but it also cools down faster in the evenings.
The figure above is a water vapor image from earlier today. Notice the red colors over the central United States? This is indicative of dry air throughout much of the atmosphere. It has been this dry air aloft, coupled with drying at the surface, that has been responsible for the warm, sunny days, and clear, cool mornings/evenings. However, a large scale trough is developing over the western United States. The flow around this trough is helping to draw tropical moisture from the eastern Pacific northward into the southwestern United States. This can be seen in animations of water vapor imagery (not shown).
As the west coast trough continues to develop, low-level moisture will be drawn northward from the Gulf of Mexico and mid/upper-level moisture will be drawn northeastward from the eastern Pacific Ocean. The increase in moisture throughout the depth of the troposphere will result in the increase in shower and thunderstorm chances across the central United States. It also means that morning and evening temperatures will not be as cool as we’ve seen the past few days. Oh well, all good things must come to an end sometime…
Day 238: 50s in August
The picture says it all. The low temperature in Norman this morning was in the upper 50s. Why can’t every summer morning be like this?
Day 237: Active Atlantic
After a relatively slow start to the Atlantic hurricane season, the Atlantic Ocean is showing signs of becoming more active. The National Hurricane Center (NHC) is currently issuing advisories on two tropical cyclones, and monitoring a third area of showers and thunderstorms for (low probability) potential for tropical cyclone development.
Hurricane Danielle (contained in yellow circle below) is currently located in the central Atlantic (southeast of Bermuda). Danielle is currently undergoing intensification, but poses no threat to the United States and only an indirect threat to Bermuda at this point. This is the result of a large trough located over the eastern United States. (Thick white dashed lines below indicate the mean long-wave trough axis.) In addition to this large trough, several smaller troughs are rotating through the larger scale flow (indicated by thin white dashed lines). This trough will tend to act like a protective barrier for the east coast. This is because of the southwesterly wind and increased wind shear that can be found on the east side of the trough. The southwesterly wind will help steer Danielle back to the north and ultimately northeast over the next few days, as was discussed on Day 234.
To the south and east of Hurricane Danielle, Tropical Storm Earl (forecast track contained in red circle) is also strengthening. This tropical cyclone is far enough removed from the previously mentioned trough, that it will have an opportunity to avoid being steered out to sea. All model guidance develop Earl into a hurricane over the next few days, and I see no reason to doubt this. Interests in the Gulf and East Coasts need to be aware of Earl as the potential will exist for a US landfall late next week. (It’s still too early to know any specifics, this is just one of many possibilities.)
In the southwestern Gulf of Mexico, the NHC is monitoring showers and thunderstorms along a remanent frontal boundary. It appears that the showers and thunderstorms will make landfall in either far south Texas or Mexico before having a change to develop into a tropical cyclone. However, to play it safe, the NHC has given a 10% chance of tropical cyclone development in this general area.
(Note: Since I didn’t describe it above, the orange contours above are 500mb height contours from the latest RUC model analysis.)
About Patrick
Patrick Marsh is a Ph.D. student at the University of Oklahoma's School of Meteorology. He earned a Bachelors of Science in Mathematics and Physics (cum laude) from the University of Arkansas in 2005 and a Masters of Science in Meteorology in 2007. In addition to working on his doctorate, Patrick serves as the National Severe Storms Laboratory Liaison to the Hazardous Weather Testbed where his research interests lie in working with operational forecasters, data mining, data visualization, and all things high-impact weather. For more about Patrick's work, check out his complete CV!
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