Day 181: Hurricane Alex Nearing Landfall
Hurricane Alex is continuing to churn close to the Mexican coast this evening, and should make landfall within the next hour as a Category 2 hurricane with winds topping 100 miles per hour. The minimum surface pressure within Alex is 947mb which is second all time for a June hurricane in the Atlantic basin. The lowest recorded Atlantic basin surface pressure is 946mb recorded in 1957 with Category 4 hurricane Audrey.
The image above (below) is of an infrared satellite image with radar mosaic overlaid (water vapor image) of Hurricane Alex. Notice in both images the presence of a well defined “eye” (warmer clouds, lighter precipitation) within the larger area of colder cloud tops.
Below two different radar images are displayed. The image on the left is the reflectivity and is what you are most likely to see when watching your local meteorologists on television. The image on the right is the velocity data, or, in other words, what the winds are doing within the rain – sort of. The velocity is determined by the radar through use of the Doppler effect. Thus, the radar can only differentiate if the wind is blowing toward or away from the radar.
Notice the line-like feature extending from the eye of Alex north toward the cyan colored letters KBRO (although the K is covered)? This “line” is known as the zero isodop. (An isodop is a line of constant Doppler velocity.) At the zero isodop, the true wind is blowing perpendicular to the radar beam and therefore the radar processor cannot tell if the particle is moving toward or away from the radar, thus the radar processor assumes a velocity of 0. Notice how as one moves away from the zero isodop line the velocity values gradually increase? This is simply because the radar beam is no longer perpendicular to the true wind and is sampling more of the toward/away component of the wind.
One small exception to this is near the eye of Alex, where the wind values increase rapidly on either side of the zero isodop? This is indicative of the rapid increase/decrease in wind speed around the eyewall of Alex. It’s typical structure for rapidly intensifying hurricanes. When examining the eye, eyewall, and surrounding area, it’s easy to notice the nearly symmetric structure displayed by Alex. This is another characteristic of a very strong, intensifying hurricane. As the residents of south Florida will tell you after hurricane Charley in 2004, it is far worse to be hit by a rapidly intensifying hurricane (such as this one) than a slightly stronger hurricane that is weakening.
Lastly, the blue boxes near Brownsville, TX indicate areas that are under a flash flood warning. This is also very typical of landfalling hurricanes. All the water that has evaporated into the hurricane to help create it must fall somewhere. Hurricanes have extremely intense precipitation rates that can easily result in places seeing over 10 inches of rain in a single day. You don’t want to even think about what happens if a hurricane stalls and lasts in a place for more than a day…
Day 180: (Officially) Hurricane Alex
It’s official; Alex has become the first hurricane in the Atlantic Basin for the 2010 Hurricane Season. In fact, Alex becomes the first June hurricane in the Atlantic Basin since 1995. The official forecast takes Alex into northern Mexico as a hurricane and then dissipates it over north-central Mexico. Far southern Texas will bear the brunt of the storm for the United States, but even this will not be as bad as it could have been (assuming the forecast track is correct). However, if you live in far southern Texas, you should be completing your hurricane preparedness plans shortly and prepare to seek appropriate shelter.
Day 179: (Soon to be) Hurricane Alex
Tonight I thought I’d share a couple more images from a new software program that is scheduled to go on sale later this summer, GREarth (authored by the creator of the Gibson Ridge radar viewers). The image above (below) is an infrared (water vapor) satellite image of Tropical Storm Alex with National Hurricane Center (NHC) forecast wind radii, track and intensity, and the Hurricane Hunter’s (which is officially known as the Air Force Reserve 53rd Weather Reconnaissance Squadron) current reconnaissance flight overlaid.
The forecast track and intensity are indicated by the circles containing the labels T (Tropical Storm) and 1 (Category 1 Hurricane). Circumscribing the forecast track and intensity labels are a funny looking circle-like objects. These “objects” are the maximum wind radii forecast by the NHC at each forecast break point. The cyan X-like object is the current flight path of the latest Hurricane Hunters reconnaissance flight. The “L” currently marks the lowest minimum pressure recorded by the Hurricane Hunters and the red arrow is the latest dropsonde information. (Although not shown in these images, the current minimum pressure is 985 mb and the strongest surface wind speed is 62 kts to the southwest of the center.)
A couple of things I’ve noticed in the last few hours is the convection redeveloping around the center of Tropical Storm Alex. This should help to strengthen Alex during the overnight. The official intensity is currently 65 mph (55 kts), so any more strengthening would bring Alex dangerously close to the hurricane threshold. In fact, the 985 mb surface pressure is more indicative of a hurricane than some previous hurricanes. I expect the wind field to catch up to the surface pressure field overnight and expect Alex to become a hurricane in the within the next 24 hours.
I should also point out that the NHC has issued a Hurricane Warning for portions of the far southern Texas coast and northern Mexico coast, including the city of Brownsville, TX. If you live in southern Texas it is time to enact your hurricane preparedness plan. If you live elsewhere along the Texas coast and/or western Louisiana, you should continue to monitor the situation closely and be prepared to activate your hurricane preparedness plan very quickly, should conditions warrant.
Day 178: A Pattern Change
With most meteorologists talking about Tropical Storm Alex, you are probably wondering why tonight’s image is a radar mosaic of the United States and not something relating to Alex. Actually, my image tonight does relate to Tropical Storm Alex. The thunderstorms depicted in the radar mosaic are developing along a cold front that is slowly moving southward across the United States. This cold front marks the leading edge of a mid-troposphere trough that is beginning to be carved out across the eastern part of the United States. This trough is replacing the ridge that has been entrenched across the central United States for the last few weeks. As I mentioned in the Day 173 post (linked above), a large ridge over the central United States is not conducive for a tropical wave to enter the Gulf of Mexico. However, a large trough over the eastern United States is conducive. Thus, the trough beginning to replace the aforementioned ridge will allow Tropical Storm Alex to turn toward the north. The all-important question then becomes, “How far north will Alex move?” The answer to this lies out west and is dependent upon what happens with the mid-troposphere pattern. Currently, a large ridge is developing / forecast to continue to develop across the western United States, coincident with the developing eastern trough. The bottom line: the weaker the ridge, the farther north Tropical Storm Alex will be able to move.
Day 177: Tropical Storm Alex
It’s official; the tropical wave I have been discussing the past few days has officially been denoted a Tropical Storm by the National Hurricane Center (NHC). Alex is the swirly looking mass of clouds located in the center of the image above. The lack of dark blue colors all the way around the center of Alex is indicative of a tropical storm, and is one reason why Alex has not developed into a hurricane. Currently, Alex has winds of around 60 miles per hour and is forecast to weaken as it moves across the Yucatan Peninsula. Once over the warm waters of the southwest Gulf of Mexico, current NHC forecasts intensify Alex to hurricane status.
I’ll repeat my message from last night. If you are anywhere along the western half of the Gulf of Mexico, please keep abreast of Alex. Be prepared to activate your hurricane preparedness plan if need be.
Day 176: Potential Alex Track
The National Hurricane Center (NHC) has classified the tropical wave discussed in Day 172 and Day 175 has now been classified as a tropical depression, the first of the Atlantic Hurricane season, with maximum sustained winds of 30 knots. It is forecast to become Tropical Storm Alex, with maximum sustained winds of 40 knots, by tomorrow afternoon. All interests in the Gulf of Mexico should continue to monitor subsequent forecasts. I’m sure I’ll have more to say about this in the coming days.
Day 175: Could We Have Alex?
As I previously mentioned on Day 172, a topical wave moving through the Caribbean Sea is continuing to move into an environment favorable for the development of a tropical system (depression/storm). Currently, the National Hurricane Center (NHC) has given this wave a 60% chance at developing into a tropical depression or tropical storm.
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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