Satellite data (Fig. 1), upper level winds (Fig. 2) and aircraft data all indicate that Alex has just about become a hurricane. Even the formation of a small eye (Fig. 3) points to this important transformation. The latest National Hurricane Center (NHC) discussion, issued at 4:00 am CDT on June 29, puts Alex’s estimated sustained winds at 70 miles per hour, just a few miles scant of hurricane status.
Alex has become a round storm on satellite imagery, indicating that upper level wind shear is almost nonexistent overhead. Still, there is a bit of elongation shown on water vapor satellite imagery (an infrared sensing channel) in a north-south direction, leading hurricane specialists to lean toward a continued drift northward for the short-term. Upper level outflow has become quite impressive over almost the storm. Some of that outflow is again passing over Florida this morning in the form of strong northerly winds at an altitude of 6 to 10 miles.
Be wary of looking at the satellite imagery and thinking that Alex is a huge storm. Much of what one sees is the upper level outflow (thick, high altitude cirrus or ice crystal clouds). A large cluster of thunderstorms has developed far to the north of the storm’s core in the central Gulf. Again, this makes the storm appear bigger than it really is. In fact, according to NHC, tropical storm force winds (39 miles per hour or more) extend only about 100 miles outward from the storm, mostly in the eastern semi-circle.
Computer models again take the storm on a west-northwest track over time (Fig. 4) as an upper level ridge starts to intensify to the north of Alex. This should occur as the stronger middle latitude system responsible for widespread severe thunderstorm activity the past two days exits the northeast.
Hence, the NHC guidance brings Alex to a landfall just south of Brownville around 1:00 am CDT on Thursday (Fig. 5) with sustained winds of nearly 100 miles per hour. This would make Alex barely a Category 2 storm at landfall.
On this track, Brownsville and the important agricultural growing region of the Rio Grande Valley will be in the leading front right quadrant of Alex. This quadrant is where the highest winds and the heaviest rainfall are often observed. Still, due to uncertainties in the storm track, hurricane warnings were posted earlier today for the Texas coast south of Baffin Bay southward through Brownsville to La Cruz on the northern Mexican coast. Hurricane warnings are now issued 36 hours in advance of when the initial tropical storm force winds are expected somewhere within the warning area. Note that coastal flooding, especially in normally flood-prone areas, may occur even before tropical storm force winds arrive.
As the storm continues inland between Thursday and Saturday, heavy rainfall over mountainous areas could lead to flash flooding in northern Mexico and/or southern Texas.
Also, note that the “cone of uncertainty” (the white envelope in which the storm track is portrayed) provides some idea of the range of geographical impact regions of the storm. It doesn’t mean that the storm couldn’t move outside the cone or that the storm won’t necessarily closely follow the central track zone. Note, too, that a hurricane or tropical storm is NOT a point on a map. Rather it is a sizable wind and wave machine.
Although Alex is not heading toward the Deepwater Horizon oil spill area, it was expected to get close enough to some drilling rigs off the Texas coast. As a result, on Sunday, BP and Shell evacuated some workers in a precautionary mode.
At this time, Alex is not expected to affect the oil spill area directly. But, as we’ve indicated here for days, waves and swells generated by Alex could move into the northern Gulf. If the waves and swells reach or are anticipated to reach this area, they may impact containment, oil collection and clean-up operations.
Current open water forecasts for the Gulf of Mexico call for the following:
Western Gulf near Alex - significant wave heights of 12 foot or more.
Central Gulf (roughly 85 degrees West longitude to 90 degrees West longitude) - 6 to 8 foot seas, building slightly over next day or so and having an added boost from swells generated, in part, from Alex.
Eastern Gulf (east of 85 degrees West longitude to 81 degrees West longitude) - seas 6 to 8 feet today but diminishing to 4 to 6 feet as Alex moves away from the area.
Because wave interaction creates wave patterns that include reinforced and interfered waves, seas are also described via “significant wave height.” Significant wave height means (in technical jargon), the average height of the highest one-third of the waves. Waves can be much above, perhaps twice as high, as the wave height indicated.
With the oil spill area relatively near Alex, it is important to view both in concert (Fig. 6). This image shows the expected track of Alex (with its “cone of uncertainty”) and the oil spill region. Note that even after 70 days of the oil spill situation (and with oil still gushing from the compromised well), wind and wave patterns have really not moved the oil very far (blue region). Current indications suggest that an eddy has developed near the spill region, further preventing (for the near term, at least) the oil from being caught in the Loop Current and spreading toward the Florida Keys and beyond.
On an even more upbeat note, we’ve waited for entertainers to finally help raise money and otherwise support the residents of the central Gulf Region in this time of need. Enter Jimmy Buffet (who often adds a weather flavor to his songs). My personal favorite is “Breathe In, Breathe Out, Move On (Crazy Man on Canal!)" in which Buffett addresses the flooding from Katrina in New Orleans.
Buffet will be holding a concert in Gulf Shores, Alabama on July 11 (postponed from July 1 due to Alex’s wave and swell potential). Tickets are no longer available for this concert, but look for other events as entertainers step up to the stage to help.
As for our weather here in southwest Florida, look for more of the same – scattered afternoon thunderstorms, favoring coastal regions due to the persistent southeast surface winds. Upper winds remain northerly, so look for thunderstorm anvils, the icy cumulonimbus tops of the storms, to spread from north to south. As noted yesterday, actual storm movement may not mimic the upper flow pattern due to local interactions amongst thunderstorms and the sea breeze. Locally heavy rains may again fall since the atmosphere overhead remains quite moist through a large depth of the troposphere (lowest 10 miles or so of our atmosphere).
Elsewhere in the tropical Atlantic Ocean, conditions remain tranquil.
For the latest official Hurricane Center advisories and discussions, click here. If you want to see the latest “spaghetti plots (the array of forecast model storm tracks), and various satellite images, click here. To view satellite derived upper level winds and see upper level steering wind patterns, click here. To see animations of cloud patterns (water vapor imagery) associated with and nearby Alex, click here.
Note that NHC routinely updates advisories every 6 hours, unless a storm is menacing a coastal area. Then advisories are issued more frequently.
© 2010, H. Michael Mogil
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