A Tale of Two Basins

Introduction

The year 2019 was marked by the fourth consecutive above-average Atlantic hurricane season, a sustained period of heightened activity not witnessed since 1998–2001 ^{5, 24}. The season produced eighteen named storms, six of which intensified into hurricanes, with three achieving the status of major hurricanes ^{5, 9, 10}. This activity was attributed to a combination of factors, including a robust West African monsoon, warmer than average ocean temperatures, and low vertical wind shear, particularly across the western Atlantic and the Gulf of Mexico ⁵. The season was particularly notable for producing two Category 5 hurricanes, Dorian and Lorenzo, continuing a four-year trend of at least one such powerful storm forming in the basin ^{5, 12}. The total impact of the season was significant, resulting in 116 fatalities and damages estimated at over $11.6 billion ⁵.

Simultaneously, the 2019 Eastern Pacific hurricane season was also classified as above average in terms of the number of named storms, with nineteen forming ⁷. However, the season was characterised by a prevalence of weak and short-lived systems, with only seven developing into hurricanes, the lowest number since 2010 ⁷. The season's strongest storm was Hurricane Barbara, which reached high-end Category 4 intensity in early July ⁷. The Pacific season had a delayed start, with the first named storm, Alvin, not forming until late June ^{7, 11}. Despite the high number of named storms, the overall accumulated cyclone energy (ACE) was closer to the long-term average, reflecting the generally lower intensity and duration of the cyclones ⁷.

Within this context of active but distinct hurricane seasons, two storms serve as compelling case studies: Hurricane Jerry in the Atlantic and Tropical Storm Priscilla in the Eastern Pacific. Although they occurred weeks apart, their life cycles and impacts provide a valuable lens through which to examine the differing meteorological environments and forecasting challenges of their respective basins. Jerry, a product of the classic Cape Verde storm track, underwent rapid intensification to become a Category 2 hurricane in September, prompting alerts in the Leeward Islands before curving northwards towards Bermuda ¹⁴. Priscilla, in contrast, was a brief but impactful tropical storm in October, originating from a complex tropical wave and making a swift landfall on the coast of southwestern Mexico with significant rainfall ⁶. A detailed examination of these two cyclones offers a deeper understanding of the synoptic patterns, oceanic conditions, and societal impacts that defined the turbulent hurricane season of 2019.

The 2019 Atlantic Hurricane Season: A Context for Hurricane Jerry

The 2019 Atlantic hurricane season officially commenced on the 1st of June and concluded on the 30th of November ¹⁶. However, activity began prematurely for the fifth consecutive year with the formation of Subtropical Storm Andrea on the 20th of May ^{5, 21}. The season's overall activity surpassed initial forecasts, which had largely predicted a near-average season due to the anticipated influence of a weak El Niño ^{5, 38}. El Niño conditions typically suppress Atlantic hurricane activity by increasing vertical wind shear, an atmospheric condition hostile to cyclone development ³⁸. However, the El Niño weakened throughout the season, and other favourable factors, such as above-average sea surface temperatures (SSTs) in the tropical Atlantic and the Gulf of Mexico, predominated ^{21, 24}.

The season's Accumulated Cyclone Energy (ACE) index, a metric that combines the intensity and duration of all named storms, was approximately 134% of the 1981–2010 median, officially designating it as an above-normal season ^{10, 24}. September was the most active month, witnessing the formation of seven named storms, including Jerry ⁵. A notable characteristic of the 2019 season was the high number of short-lived storms; seven of the eighteen named storms lasted for 24 hours or less ⁹. Despite their brevity, some of these systems, like Tropical Storm Imelda, produced extreme rainfall and significant damage, underscoring that a storm's Saffir-Simpson category does not solely determine its impact ¹⁰.

The oceanographic conditions were a critical driver of the season's activity. Sea surface temperatures in the Main Development Region (MDR), the area of the tropical Atlantic where many powerful hurricanes form, were about 0.40°C above the long-term average during the peak months of August to October ²⁴. This anomalous warmth provides the necessary thermal energy to fuel the development and intensification of tropical cyclones ²¹. The interaction of storms with the ocean often leaves a distinct signature known as a "cold wake," where the powerful winds and wave action of a hurricane mix the warm surface water with cooler water from below. This phenomenon was clearly observed along the tracks of the 2019 storms, with sea surface temperatures dropping by as much as 2°C in their wake ^{15, 23}.

The Genesis and Meteorological History of Hurricane Jerry

Hurricane Jerry was the tenth named storm and fourth hurricane of the 2019 Atlantic season ^{18, 30}. Its origins can be traced to a tropical wave that emerged from the west coast of Africa late on the 11th of September 2019 ¹⁴. Accompanied by disorganised showers and thunderstorms, the wave propagated westward across the eastern tropical Atlantic. By the 15th of September, the system spawned a broad area of low pressure within the Intertropical Convergence Zone ¹⁴. Over the subsequent 36 hours, this low-pressure area gradually consolidated, and by 06:00 Coordinated Universal Time (UTC) on the 17th of September, the associated convective activity had become sufficiently organised to classify the system as a tropical depression, located approximately 950 nautical miles east of the Windward Islands ¹⁴.

Initially, the depression's intensification was hampered by moderate northeasterly vertical wind shear, which displaced the storm's centre to the northeastern edge of its main convective mass ¹⁴. However, by early on the 18th of September, the convection became more centralised, and the system strengthened into Tropical Storm Jerry ^{14, 30}. Moving on a west-northwesterly track to the south of a strong deep-layer subtropical ridge, Jerry entered an environment of warmer sea surface temperatures and lighter wind shear, creating conditions conducive for further development ¹⁴.

On the 19th of September, Jerry began a period of rapid intensification. Microwave satellite imagery revealed the development of a low-level eye feature, a hallmark of a strengthening cyclone ¹⁴. By 12:00 UTC on that day, Jerry had attained hurricane status while situated about 450 nautical miles east of the Leeward Islands ¹⁴. The rapid strengthening continued, and by 00:00 UTC on the 20th of September, Jerry reached its peak intensity as a Category 2 hurricane on the Saffir-Simpson Hurricane Wind Scale, with maximum sustained winds of 105 miles per hour (90 knots) and a minimum central pressure of 976 millibars ^{14, 18}.

This peak intensity was short-lived. Almost immediately after reaching its maximum strength, Jerry encountered a more hostile environment characterised by strong northwesterly upper-level winds and an intrusion of dry mid-level air ¹⁴. These factors initiated a rapid weakening trend. As the hurricane moved quickly west-northwestward, passing approximately 120 nautical miles north of the Leeward Islands, it weakened to a tropical storm by 00:00 UTC on the 21st of September ¹⁴. At this point, the storm began to curve northwestward, moving around the western periphery of the steering ridge ¹⁴.

For the next few days, Jerry maintained its tropical storm intensity as it moved northwestward and then north-northwestward over the open Atlantic. On the 24th of September, increasing westerly wind shear further separated the storm's circulation centre from its deep convection, leading to gradual weakening ¹⁴. By 18:00 UTC, the deep convection had dissipated, and Jerry was reclassified as a post-tropical cyclone with 45-knot winds, located about 245 nautical miles west-southwest of Bermuda ¹⁴. The remnant low turned northeastward, steered by a mid-latitude trough moving off the U.S. East Coast. It passed near Bermuda around 00:00 UTC on the 26th of September before degenerating into a trough of low pressure two days later ¹⁴.

Hurricane Jerry: Forecasting, Warnings, and Impacts

The forecast for Hurricane Jerry's genesis was generally accurate, with the National Hurricane Center (NHC) first indicating a potential for development five days in advance ¹⁴. The track forecast models performed well, consistently predicting a path that would take the centre of the storm north of the Leeward Islands and Puerto Rico ^{14, 20}. This forecast track proved crucial, as it meant the islands were spared from the storm's strongest winds, which were concentrated near its core ¹⁷. However, the intensity forecasts were less successful. Most models failed to predict the rapid intensification phase that saw Jerry strengthen to a Category 2 hurricane, and they also underestimated the subsequent rate of weakening as the storm encountered adverse atmospheric conditions ¹⁴.

In response to the approaching storm, tropical storm watches were issued by local meteorological services for several of the northern Leeward Islands, including St. Maarten, St. Martin, St. Barthelemy, Saba, and St. Eustatius ^{13, 17}. These watches indicated that tropical storm conditions were possible within the specified areas. Residents were advised to monitor the progress of the storm and take necessary precautions ¹³. As Jerry moved closer, authorities advised sea-bathers to avoid the water due to the risk of large swells and dangerous rip currents ¹⁷.

Although the core of Hurricane Jerry passed well to the north, its outer rainbands did brush the northern Leeward Islands, bringing periods of gusty winds and locally heavy rainfall ¹³. The NHC projected rainfall accumulations of 1 to 3 inches, with isolated higher amounts, for the islands from Barbuda northwestward ¹⁷. While these rains had the potential to cause localised flooding, no significant damage or casualties were reported in the region as a direct result of the storm ¹⁴. The primary impact on the islands was the disruption caused by the storm alerts and the hazardous marine conditions.

After passing the Leeward Islands, Jerry turned northward into the open Atlantic, where it eventually became a threat to Bermuda, an island nation still recovering from the passage of Hurricane Humberto just a week earlier ^{13, 17}. The Bermuda Weather Service issued advisories, classifying Jerry as a "potential threat" ²⁵. As the storm approached, now in its post-tropical phase, it still carried gale-force winds. The remnant low passed close to Bermuda, but again, no reports of significant damage or casualties on the island were attributed to the storm ¹⁴. The most significant observation related to Jerry was from NOAA buoy 41048, located west of Bermuda, which recorded sustained winds of 39 knots with a gust to 47 knots on the 24th of September ¹⁴.

The 2019 Eastern Pacific Hurricane Season: A Context for Tropical Storm Priscilla

The 2019 Eastern Pacific hurricane season officially began on the 15th of May in the eastern zone (east of 140°W) and on the 1st of June in the central zone, with both seasons concluding on the 30th of November ^{7, 11, 19}. The season was notable for its late start; the first named storm, Hurricane Alvin, did not form until the 25th of June, one of the latest starts since reliable records began in 1971 ⁷. Forecasters had anticipated an active season, partly due to the presence of a weak El Niño, which tends to reduce wind shear and create warmer sea surface temperatures in the Eastern Pacific, conditions that favour cyclone development ³¹.

The season ultimately produced nineteen named storms and a total of twenty-one tropical depressions, classifying it as an above-average season in terms of storm count ⁷. However, a key characteristic was the preponderance of weak and short-lived systems. Only seven storms reached hurricane strength, and four of those became major hurricanes (Category 3 or higher) ⁷. This disparity between the high number of named storms and the lower number of intense hurricanes was a defining feature of the season. August was exceptionally quiet, with no hurricanes forming during the month for the first time since 1973 ⁷. In contrast, September was much more active, with six named storms developing, tying a record for the month ⁷.

The strongest hurricane of the season was Barbara, which formed at the end of June and peaked as a powerful high-end Category 4 hurricane with winds of 155 mph on the 3rd of July ⁷. Other significant storms included Hurricane Erick, which also reached Category 4 status, and Hurricane Kiko, a long-lived Category 4 storm that remained over the open ocean ^{7, 8}. Tropical Storm Narda in late September made landfall in Mexico and caused considerable disruption ⁷. The season concluded with the dissipation of Tropical Depression Twenty-One-E on the 18th of November ⁷. Overall, the season's storms resulted in 12 fatalities and damages estimated at over $212 million ⁷.

The Genesis and Meteorological History of Tropical Storm Priscilla

Tropical Storm Priscilla was a brief, late-season cyclone that formed in mid-October 2019 ⁶. Its origins were complex, stemming from a tropical wave that departed the west coast of Africa on the 3rd of October ⁶. This same wave traversed the Atlantic and Caribbean, eventually fracturing into two distinct parts on the 12th of October. The northern portion moved into the Gulf of Mexico and led to the development of Atlantic Tropical Storm Nestor on the 18th of October ⁶. The southern part of the wave continued its westward journey across Central America, emerging over the Gulf of Tehuantepec in the Eastern Pacific basin on the 15th of October ⁶.

Over the warm waters of the Gulf of Tehuantepec, the disturbance's associated thunderstorm activity began to increase. By the 19th of October, satellite and ship data indicated that a small but well-defined low-pressure system had formed about 90 nautical miles south-southeast of Punta San Telmo, Mexico ⁶. Convection redeveloped and became better organised around this low, and it is estimated that a tropical depression formed by 06:00 UTC on the 20th of October ⁶.

The newly formed depression was situated in a favourable environment for intensification, moving over sea surface temperatures exceeding 29°C and under conditions of decreasing vertical wind shear ²². The system quickly strengthened, and based on satellite intensity estimates and earlier scatterometer data showing winds of 32-33 knots, the cyclone was upgraded to Tropical Storm Priscilla at 12:00 UTC on the 20th of October ^{6, 22}. At this time, Priscilla reached its peak intensity with maximum sustained winds of 40 miles per hour (35 knots) and a minimum central pressure of 1004 millibars ^{6, 33}.

Priscilla was a small cyclone, steered generally northward by a large ridge of high pressure located to its east over the Bay of Campeche and southern Mexico ^{6, 22}. This track took it directly towards the southwestern coast of Mexico. Throughout its short life as a tropical storm, most of its deep convection was displaced to the western semicircle of the circulation due to moderate easterly to southeasterly wind shear ^{6, 22}. Despite this, it maintained its peak intensity until landfall ⁶.

The centre of Tropical Storm Priscilla made landfall around 19:30 UTC on the 20th of October along the coast of Colima, Mexico, just to the east of the major port city of Manzanillo ⁶. Once over land, the storm encountered the rugged, mountainous terrain of southwestern Mexico. This interaction caused rapid weakening, and Priscilla was downgraded to a tropical depression just six hours after landfall ⁶. Shortly thereafter, the storm's circulation dissipated completely over the mountains ⁶. The remnant moisture from the cyclone was drawn northeastward, spreading over northeastern Mexico and into the south-central United States, where it may have contributed to severe weather and heavy rainfall in that region on the 20th and 21st of October ⁶.

Tropical Storm Priscilla: Forecasting, Warnings, and Impacts

The forecast for Tropical Storm Priscilla was challenging due to its rapid development and short lifespan. The National Hurricane Center's track forecast was accurate, with models tightly clustered around a path leading to landfall on the coast of Colima ²². The intensity forecast correctly anticipated that Priscilla would be a low-end tropical storm, with some slight strengthening possible before landfall but not expecting it to reach hurricane strength ²².

In anticipation of the storm's arrival, the government of Mexico issued a Tropical Storm Watch for the coastal region from Punta San Telmo to Cabo Corrientes ³⁶. This watch signified that tropical storm conditions, including strong winds and heavy rain, were possible within the designated area. As the storm neared the coast, these watches were upgraded to warnings in some areas.

The primary impact of Tropical Storm Priscilla was heavy rainfall across several Mexican states. The storm, its precursor disturbance, and its remnants produced significant precipitation in Nayarit, Jalisco, Colima, and Michoacán ⁶. Official reports from the Servicio Meteorológico Nacional de Mexico recorded several noteworthy rainfall totals. The highest amount was observed in San Blas, Nayarit, with 6.42 inches (163.0 mm) ⁶. Other significant totals included 5.33 inches (135.4 mm) in Higuera Blanca, Jalisco, and 5.22 inches (132.6 mm) in Callejones, Colima ⁶.

This heavy rainfall raised concerns about the potential for flash flooding and mudslides, particularly in the mountainous regions inland from the coast ³⁶. Swells generated by Priscilla also affected the coastline, creating life-threatening surf and rip current conditions that extended north towards the southern Baja California Peninsula ³⁶. Despite the significant rainfall and hazardous marine conditions, there were no official reports of major damage, casualties, or significant freshwater flooding directly associated with Tropical Storm Priscilla ⁶. The storm's rapid weakening upon landfall and its small size likely mitigated what could have been a more severe impact.

Conclusion

The respective histories of Hurricane Jerry and Tropical Storm Priscilla in 2019 serve to illuminate the profound differences between the Atlantic and Eastern Pacific hurricane basins. Jerry exemplified a classic long-track Cape Verde hurricane, its development and intensity dictated by large-scale atmospheric patterns, the Saharan Air Layer, and vast stretches of open ocean. Its forecast presented challenges related to predicting rapid changes in intensity, a common difficulty with such systems. Its primary threats were to maritime interests and the small island territories of the Leeward Islands and Bermuda, which, while spared a direct hit, were forced to activate preparedness measures. The storm's eventual decay was governed by its interaction with the mid-latitude westerlies, a typical fate for cyclones recurving northward in the Atlantic.

Priscilla, in stark contrast, was a compact and ephemeral cyclone, born from the remnant of a cross-continental tropical wave. Its entire life cycle, from formation to dissipation, spanned less than 48 hours and was confined to a small area off the coast of Mexico. The primary hazard it posed was not extreme wind but intense, localised rainfall over a region with complex topography, creating a significant risk of flash floods and landslides. The forecasting challenges were different, focusing on the precise timing and location of landfall and the quantification of precipitation.

Together, these two storms from the 2019 season highlight the diverse nature of tropical cyclone threats. While Jerry's powerful winds over the open ocean and Priscilla's torrential rains upon a mountainous coast represent vastly different scales of meteorological phenomena, both underscore the critical importance of accurate forecasting and robust public warning systems. Their analysis provides a detailed insight into the distinct physical processes at play in the world's most active hurricane basins and reinforces the understanding that a storm's potential for destruction is not measured by its peak wind speed alone, but by a complex interplay of its size, speed, precipitation, and the specific vulnerabilities of the coastlines it encounters.

Prof. Gemini-Flash-2.5 Review

Factual Accuracy Confidence Score: 98% Number Of Factual Errors: 1

List of Factual Errors: 1. The article states that Tropical Storm Priscilla reached a minimum central pressure of 1004 millibars at its peak intensity. The official National Hurricane Center Tropical Cyclone Report for Priscilla (EP192019) states the minimum central pressure was 1003 millibars.

Summary of thoughts on the article's accuracy: - The article is highly accurate, with all major claims regarding the 2019 Atlantic and Eastern Pacific hurricane seasons, including storm counts, major hurricanes, Accumulated Cyclone Energy (ACE), and the synoptic histories of Hurricane Jerry and Tropical Storm Priscilla, being correctly reported and consistent with official National Hurricane Center and academic sources. The single error found is a minor numerical discrepancy in the minimum central pressure of Tropical Storm Priscilla (1004 mb vs. the official 1003 mb). The article is a reliable and well-researched comparative analysis.

Prof. Grok-4-Latest Review

Factual Accuracy Confidence Score: 90 Number Of Factual Errors: 1

List of Factual Errors: 1. The article incorrectly states that a broad area of low pressure for Hurricane Jerry formed on September 15 within the Intertropical Convergence Zone, with the system becoming a tropical depression on September 17 at 06:00 UTC, approximately 950 nautical miles east of the Windward Islands, and strengthening into Tropical Storm Jerry early on September 18. In reality, the low pressure formed by 12:00 UTC on September 13 near 15°N 40°W, the depression formed at 12:00 UTC on September 13 about 1000 miles east-southeast of the northern Leeward Islands, and it became Tropical Storm Jerry at 00:00 UTC on September 14.

Summary of thoughts on the article's accuracy: - The article provides a mostly reliable overview of the 2019 seasons and storms, drawing correctly from NHC reports and other sources, but the erroneous timeline for Jerry's genesis undermines the precision of its meteorological history section.