September saw yet another 6 systems form in a very active 2005 season. By the end of the month, 19 tropical depressions and 17 named tropical storms had formed -- well above normal for an entire season, yet alone before the secondary peak in activity for a normal season. All but one of this month's systems became hurricanes, with one of them ranking in the list of the 5 most intense storms of all time. Let's start from the beginning...
As Lee died out over the open waters of the North Atlantic, the system that would spawn Maria was getting organized to its south. A tropical depression formed from a tropical wave at a fairly high latitude in the central Atlantic on September 1st, organizing into Tropical Storm Maria on September 2nd. Maria intensified at quite a fast rate over the next two days as it headed toward the northwest over open waters, becoming a hurricane early on September 4th and a major hurricane briefly late on September 5th as it turned to the north well east of Bermuda. Maria was captured by a midlatitude trough and began to accelerate toward the northeast thereafter, weakening down to a tropical storm on September 7th. It strengthened again to a category 1 storm as it began to accelerate and the storm-relative shear weakened, only to weaken again to a tropical storm late on September 8th before becoming in the northern Atlantic early on September 10th.
During the midst of Maria's lifetime, another tropical system was getting organized south-southwest of Bermuda, likely enhanced by a nearby upper-level low pressure system. Late on September 5th, this system became a tropical depression, later becoming Tropical Storm Nate as the 5th headed into the 6th. The system initially headed toward the east-northeast toward Bermuda while becoming organized at a fairly good clip. As Nate turned more toward the northeast, passing well south of Bermuda, it intensified into a minimal hurricane on September 7th. It held steady in intensity as it headed generally toward the northeast over open water, gradually bending toward the east-northeast. On September 9th, Nate weakened to a tropical storm and subsequently turned toward the east. By midday on September 10th, Nate became , largely in advance of the same trough that captured Maria further to the north.
Around the same time that Nate was organizing, we had yet another system getting going near the Bahamas, spun off on the northeast side of an upper-level area of low pressure north of the islands much like several other storms (notably Franklin and ) before it. A tropical depression formed during the day on September 6th north of the northern islands, slowly organizing into a tropical storm -- Ophelia -- early on September 7th. Model guidance was quite divergent with this storm from the beginning, with some models calling for recurvature over open waters offshore of the SE US and others calling for a track across central Florida toward the Florida panhandle. Over the next few days, however, Ophelia moved erratically and slowly toward the north-northwest, leaving many along the southeast US coastline under the gun for some period of time. Interesting anecdote -- I was at the -Citadel football game during the time that Ophelia had South Carolina under the gun. They accounced at the game that Citadel students were not to return to SC over the weekend or early into the next week during Ophelia -- this drew the biggest cheer all game long from a fan base that had little to cheer about and a crowd that had little to cheer about during the 2005 hurricane season.
Nevertheless, as Ophelia approached the northern Florida coastline, it stalled out while briefly reaching hurricane intensity on September 8th. Due to upwelling, it weakened briefly thereafter back to a tropical storm on September 9th before reacquiring hurricane intensity later that day as it bgan to parallel the coastline from afar. However, the storm would again stall out well to the SE of Myrtle Beach, SC. As it did so, the convective pattern with Ophelia deteriorated as the storm began to feel the impacts of upwelling once again. Nevertheless, the storm maintained minimal hurricane intensity for quite sometime offshore before beginning to head to the west-northwest as a strong tropical storm on September 12th. Ophelia made it's closest approach to shore on September 14th, again as a minimal hurricane, scraping the southeastern NC shoreline as it did so. It reached its peak intensity late that evening of 80kt/979mb before accelerating toward the northeast and gradually weakening as it paralleled the US coastline. Ophelia was operationally declared as September 17th became September 18th is it approached the Canadian Maritimes as a moderate tropical storm. Despite never quite making landfall officially, Ophelia is attributed to $1.6 billion in US damages, largely from beach erosion in its 12 days paralleling the SE US coastline.
Phillipe was next up in the active hurricane season, forming east of the Lesser Antilles as Ophelia began to become . The initial forecasts called for some substantial development of the tropical depression that formed on September 17th, and indeed we did see a tropical storm form late on September 17th and a hurricane form late on September 18th as the storm drifted to the north-northwest paralleling the Lesser Antilles. Phillipe reached its peak intensity early on September 20th at 70kt/985mb while east of the northern Lesser Antilles, but never came close to reaching the initial projections for it. A very strong upper-level low formed to the west of the storm, enhanced by the strong westerly flow associated with a strong ridge of high presssure to the north and the easterly outflow from another developing storm -- , more on this in a minute -- to the south. This feature served to shear Phillipe, resulting in an asymmetric system that weakened into a tropical storm late on September 20th. This storm quickly weakened into a weak tropical storm, heading generally to the north around the eastern periphery of the upper-low before being forced back to the west under the influence of the aforementioned upper-ridge. As Phillipe began to approach Bermuda, it quickly dissipated late on September 23rd south of the island.
This month's big feature was the aforementioned . formed in much the same manner as , albeit without enhancement from remnants of a previous tropical depression, in the vicinity of the Bahamas, on Septemnber 18th. followed a generally north of due west path toward the southern part of Florida over the next few days, gradually getting organized as it did so. Due to interaction with land and weak wind shear, it never could quite get organized before reaching the southeastern Florida Keys early on September 20th as a strong tropical storm. However, as it passed south of Key West, it quickly intensified into a hurricane on September 20th and became a major hurricane early on September 21st. Early model projections thankfully spared New Orleans yet targeted areas of the central Texas coastline. But, as with , these projections would require some revision after a burst of rapid intensification, perhaps due to poor model representation of such a strong storm until the point that it reached category 5 intensity. This is another topic left for a research project, however. Nevertheless, in the period from 0600 UTC to 2100 UTC on the 21st of September, as passed along the edge of a warm eddy in the central Gulf of Mexico, it rapidly intensified from a 100kt category 3 storm to a 145kt category 5 storm.
There was much uncertainty as to how much could intensify, as no one truthfully knew how much of an impact had on the very favorable oceanic conditions in the central Gulf. showed us how little we know about this, unfortunately, as it became (at the time) the 3rd most intense storm on record in the Atlantic basin with a pressure of 897mb (150kt) as the night of the 21st became the morning of the 22nd in the central Gulf of Mexico. Around the same time, model guidance suggested that could be the 'big one' for the Galveston/Houston area of Texas, unlike anything they had seen since the infamous storm of 1900, prompting evacuations for the entire region. Model guidance would slowly shift further toward the north, however, sparing those areas the worst of the storm.
From here on out, inner core fluctations such as eyewall replacement cycles dominated the intensity profile of the storm, with a gradual weakening seen toward landfall as the storm moved toward the west, then northwest, and finally north-northwest across the central and western Gulf of Mexico. ultimately made landfall as a 105kt category 3 hurricane near the Texas/Louisiana border overnight on September 24th, resulting in heavy damage across western Louisiana and extreme eastern Texas -- not to mention flooding of low-lying areas of New Orleans no longer protected by levees after Hurricane . After landfall, began to slow and weaken rapidly, becoming a tropical storm midday on September 24th and a tropical depression late that evening. was responsible for quite a bit of rainfall in the ArkLaTex region and, per the , resulted in 6 deaths and $9.4 billion in US damage. To that point in the season, this would have placed the storm as the 5th costliest storm in US history (in unadjusted dollars), only behind , Andrew, , and and just ahead of .
Late in the month, as Cape Verde season typically winds down, we saw the furthest-east tropical origin system form for the 2005 season, Tropical Depression 19, late on September 30th. In the midst of a marginally favorable environment -- largely limited by vertical wind shear, particularly in the mid-levels -- little development was seen from the depression before it dissipated on October 2nd. Were it not for several atypical subtropical tropical cyclones that would develop later in the season, TD 19 would hold the honor of furthest-east development in the atypical 2005 season. Nevertheless, it set the stage for a very active October, where 7 storms formed (well above average), which we'll take a look at next time.
--------------------
Current Tropical Model Output Plots
(or view them on the main page for any active Atlantic storms!)
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
