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Subtropical Depression Isaias
Subtropical Depression (SSHWS/NWS)
Isaias 2032 Sim (Zeta).png
Subtropical Depression Isaias shortly before landfall in Louisiana
FormedJuly 8, 2032
DissipatedJuly 16, 2032
(Post-tropical after July 14)
Highest winds1-minute sustained:
35 mph (55 km/h)
Lowest pressure1009 mbar (hPa); 29.8 inHg
Fatalities42 direct, 6 indirect
Damage$1.2 billion (2032 USD)
Areas affectedLouisiana, Texas, Mississippi, Arkansas, Alabama, Tennessee, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, New Jersey, Massachusetts, Rhode Island
Part of the 2032 Atlantic hurricane season


Subtropical Depression Isaias was a disorganized, but long-lived and destructive subtropical cyclone that formed in the Gulf of Mexico in July. The tenth (sub)tropical depression of the extremely active 2032 Atlantic hurricane season, Isaias's slow and winding path led to widespread flooding and a tornado outbreak across the northern Gulf Coast and southeastern United States. While Isaias was operationally considered to have attained tropical storm-force winds, and thus received a name, the National Hurricane Center's routine post-season analysis concluded that it instead had lost its subtropical characteristics before it attained gale-force winds; as a result, Isaias remains one of the few (sub)tropical cyclones to receive a name but peak at depression status.

Isaias began as a low pressure area in the Bay of Campeche being monitored by the National Hurricane Center for possible development. It acquired subtropical characteristics, albeit slowly, and was designated Potential Tropical Cyclone Ten on July 7 due to its proximity and threat to land. Numerous tropical storm watches were put up for portions of Louisiana in anticipation of the storm attaining tropical storm-force winds. The next day, the low was determined to have become a subtropical depression, and thus it was designated as such by the NHC. The depression's slow forward speed resulted in many forecasts that predicted it to become a named storm, but instead it maintained subtropical depression status all the way to landfall. Then known as Subtropical Depression Ten, the storm tracked in a steadily westward direction but eventually took a gradual turn eastward, remaining a subtropical cyclone for an unusually long amount of time over land. Over North Carolina, Subtropical Depression Ten, operationally still considered to have been a subtropical cyclone, acquired gale-force winds, resulting in the naming of the cyclone as Subtropical Storm Isaias in the following NHC advisory. However, because the post-season analysis determined Isaias had already lost its subtropical characteristics before attaining the aforementioned gale-force winds, its status has been downgraded to a subtropical depression.

High rainfall totals occurred across the Gulf Coast and southeastern United States, with over 30" of rain in some locations. While Isaias's gradual curve to the west prior to landfall likely prevented damage from being as severe in the New Orleans area, its bands still produced moderate to severe flooding across much of the region. In total, Isaias caused about $1.2 billion (2032 USD) in damage and resulted in 42 direct deaths, along with 6 indirect deaths. Despite the damage caused by Isaias, the name was not retired.

Meteorological history

Map plotting the track and intensity of the storm, according to the Saffir-Simpson scale

On July 2, The National Hurricane Center noted the possible formation of a low pressure area over the Bay of Campeche or Gulf of Mexico. However, due to above-average wind shear, the potential low was not expected to have any significant development. Confidence in the low's formation increased over the next two days, and it finally formed on the 4th. Soon known as Invest 94L, the low moved northward at a sluggish pace but began to attain subtropical characteristics. Because tropical storm watches were deemed necessary, 94L was further designated as Potential Tropical Cyclone Ten. One day later, Ten was considered to have been organized enough to be deemed a subtropical cyclone, and as such, it was classified as a subtropical depression with winds of 35 mph (56 km/h) and a minimum barometric pressure of 1009 mbar (29.80 inHg).

Isaias when operationally assessed as a subtropical storm over North Carolina; later found out to have been a post-tropical cyclone

Subtropical Depression Ten showed little change in appearance or intensity over the next 24 hours as it approached landfall. On July 9, at approximately 02:00 UTC, the depression made landfall over Louisiana at peak intensity. It curved in a westward direction and maintained its organization and appearance, producing deep convective bursts and maintaining its subtropical characteristics despite being over land. This has since been attributed to the Brown Ocean Effect. Ten had a very slow forward speed, resulting in torrential rains over the area.

Ten continued to move at a very slow pace but began to turn eastward, finally exiting Louisiana on July 12. It started to accelerate east-northeastward and became increasingly disorganized. The National Hurricane Center's Tropical Cyclone Report on the storm indicated that it became a post-tropical low over eastern Georgia; however, operationally, it was considered to have still been a subtropical cyclone. Over North Carolina, Ten's remnants attained gale-force winds, but because the National Hurricane Center retained its subtropical classification in real-time, it was declared a subtropical storm and was given the name Isaias. Operationally, this stint as a subtropical storm was short-lived, as the NHC's next advisory was its last due to it having been recognized as post-tropical. The gale-force remnants of Isaias moved offshore on July 15 and soon weakened, dissipating the following day.

Preparations

The precursor to Isaias, located in the Gulf of Mexico

In Isaias's first several advisories as a potential tropical cyclone and subtropical depression, the National Hurricane Center's forecast advisories and discussions predicted that the storm would intensify into a subtropical storm at landfall. Because of this, tropical storm watches were put up for portions of Louisiana's coast, and they were later upgraded to warnings. However, as the storm failed to meet its forecast, the watches and warnings were quickly discontinued.

Because Isaias was operationally assessed to have become a subtropical storm over North Carolina, tropical storm warnings were hastily put in place for the area; however, its operational state as a subtropical storm only lasted three hours, and the warnings were discontinued shortly thereafter.

The storms' outer bands resulted in the issuance of numerous flash flood watches and warnings, and a tornado outbreak took place across the southeastern United States for about 19 hours. A total of 14 tornadoes formed in this timespan, the strongest of which was rated at EF-2 intensity. Because of this outbreak, several counties were put under tornado watches and warnings.

Impact

Louisiana

Isaias passed through Louisiana for over three days, resulting in torrential downpours and severe flooding. Of the $1.2 billion in damage that the storm caused, about $900 million of it was attributed to damage in the state of Louisiana. Rainfall accumulations were estimated to have reached over 30" in some locations, and the resulting floods generated the majority of Isaias's damage. Thousands of houses were considered damaged beyond repair, and 27 direct deaths occurred in the state, roughly half of which were from drowning. Overall, damage ranged from moderate to severe across the state.

Texas

While Subtropical Depression Isaias's circulation never passed through Texas, rain bands moved through the state for many days. There was light to moderate flooding in the eastern part of Texas, with rainfall maximums around 12". While two indirect deaths occurred from hydroplaning accidents, damage was generally minimal in Texas, with about $230,000 being attributed to Isaias.

Mississippi

Isaias's circulation moved through the state of Mississippi much faster than it did through Louisiana, but the western part state still suffered the rain bands of the storm while it nearly stalled over Louisiana. Accumulations of rainfall reached about 27", and about $120 million in damages occurred throughout the state. In addition to this, moderate flash flooding took eight lives. Furthermore, two more indirect deaths occurred in Mississippi, another of which was due to hydroplaning, and the other of which was from carbon monoxide poisoning. Damage was overall moderate in Mississippi.

Southeastern United States

The southeastern United States did not face nearly as much damage as Louisiana did, but notable flooding and a tornado outbreak occurred. Two deaths resulted from the associated tornado outbreak. In addition, seven more direct fatalities were associated with Isaias; all of these were related to the flooding that ensued after the rainfall. About $180 million in damage occurred in the southeastern United States, and overall damage was moderate.

Mid-Atlantic and Northeast United States

Little damage occurred in the Mid-Atlantic and northeastern parts of the United States with the exception of gale-force winds from Isaias's remnants affecting some regions. Overall, however, Isaias had little effect on the regions, and no deaths occurred.

Aftermath

Isaias resulted in power outages across the Gulf Coast and eastern United States, the longest of which lasted about seven days. Despite the damage caused by Isaias, the name was not retired, making it one of the costliest (sub)tropical cyclones to not have their names retired.

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