Luis M. Farfán

Moving and Stationary Mesoscale Convective Systems over Northwest Mexico during the Southwest Area Monsoon Project

Abstract Some characteristics of the life cycle and motion of Mesoscale Convective Systems (MCSs), which formed over the northern Sierra Madre Occidental during the Southwest Area Monsoon Project (SWAMP), are examined. The motion characteristics of MCSs and presence of residual circulations (mesoscale vortices) are determined using Geostationary Operational Environmental Satellite infrared and visible satellite imagery. Composite wind fields associated with moving and stationary systems were constructed using soundings from the operational upper-air network and from special pilot balloon stations that were operated in Mexico as part of the SWAMP experiment. The MCSs were classified as moving or stationary based on the observed displacement during a 6-h period. Moving and stationary systems occurred with about the same frequency. The moving systems were distributed uniformly along the length of the Sierra Madre, while the stationary systems were primarily confined to the southern Gulf of California. The st...

Orographic Influence on the Synoptic-Scale Circulations Associated with the Genesis of Hurricane Guillermo (1991)

Abstract The early stages of tropical cyclogenesis in the eastern Pacific Ocean are investigated in this case study, which is focused on the development of the initial circulation that eventually intensified into Hurricane Guillermo (1991). The authors document the synoptic and mesoscale winds from upper-air soundings, satellite imagery, and a gridded analysis. In addition, flight-level observations taken during the Tropical Experiment in Mexico are used. These winds reveal that, prior to the formation of the tropical cyclone, an easterly wave moved over the Caribbean Sea and that the initial circulation developed while the easterly wave was located over the central Caribbean, east of the mountains in Central America. Numerical simulations with the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model are used to examine the details of the structure of the flow that resulted in the formation of the eastern Pacific circulation. In these simulations, the model is initialized...

Influence of Tropical Cyclones on Humidity Patterns over Southern Baja California, Mexico

Abstract The influence of tropical cyclone circulations in the distribution of humidity and convection over northwestern Mexico is investigated by analyzing circulations that developed in the eastern Pacific Ocean from 1 July to 21 September 2004. Documented cases having some impact over the Baja California Peninsula include Tropical Storm Blas (13–15 July), Hurricane Frank (23–25 August), Hurricane Howard (2–6 September), and Hurricane Javier (15–20 September). Datasets are derived from geostationary satellite imagery, upper-air and surface station observations, as well as an analysis from an operational model. Emphasis is given to circulations that moved within 800 km of the southern part of the peninsula. The distribution of precipitable water is used to identify distinct peaks during the approach of these circulations and deep convection that occurred for periods of several days over the southern peninsula and Gulf of California. Hurricane Howard is associated with a significant amount of precipitatio...

Regional Observations during the Landfall of Tropical Cyclone Juliette (2001) in Baja California, Mexico

Abstract This paper presents an observational analysis of tropical cyclone landfall over the eastern Pacific Ocean. The tropical cyclone that developed during the 2001 season off the Mexican coast was named Juliette and made landfall in the Baja California peninsula. Juliette approached land over the southwestern peninsula, and the evolution of a localized region of cyclonic circulation occurred over the Gulf of California. The storm passage was associated with extensive property damage to the population in the southern peninsula, with most of the damage caused by heavy rainfall and strong winds. The intensity of the circulation associated with Juliette indicates that this was a strong system in the record of landfall during the period 1992–2002. All available sources of observations are collected to investigate characteristics of the circulation motion and structure. In situ observations, including surface and upper-air data, are applied to document the evolution of storm flow while the center was locate...

Landfalling tropical cyclones on the Pacific coast of Mexico: 1850-2010

Historical documents and newspapers from Mexican Pacific states (north of 14o N) were reviewed to determine the incidence of landfalling tropical cyclones from 1850 to 1949, prior to the start of the United States National Hurricane Center database. The reviewed documents are only found in Mexican repositories at national, state and municipal level and the systematic search embarked upon in this study yielded valuable information that cannot be found elsewhere. A time series of landfall was reconstructed back to 1850, indicating active and quiet periods. An average of 1.8 ± 1.6 landfalls per year is determined from the time series for 1850-2010. When the series is limited to 1880-2010, eliminating the first 30 years that may have some undercounting, the average increases to 2.1 ± 1.6 cases per year. Spectral and wavelet analysis of the 161 years of landfalling tropical cyclones indicates that the Pacific Decadal Oscillation (PDO) modulates the activity. The influence of El Nino/Southern Oscillation(ENSO) and the North Atlantic Oscillation (NAO) on the landfall frequency may be present throughout the reconstruction period but both oscillations have lower correlations compared to that from the PDO.

An Observational and Modeling Analysis of the Landfall of Hurricane Marty (2003) in Baja California, Mexico

Abstract This paper documents the life cycle of Tropical Cyclone Marty, which developed in late September 2003 over the eastern Pacific Ocean and made landfall on the Baja California peninsula. Observations and best-track data indicate that the center of circulation moved across the southern peninsula and proceeded northward in the Gulf of California. A network of surface meteorological stations in the vicinity of the storm track detected strong winds. Satellite and radar imagery are used to analyze the structure of convective patterns, and rain gauges recorded total precipitation. A comparison of Marty’s features at landfall, with respect to Juliette (2001), indicates similar wind intensity but differences in forward motion and accumulated precipitation. Official, real-time forecasts issued by the U.S. National Hurricane Center prior to landfall are compared with the best track. This resulted in a westward bias of positions with decreasing errors during subsequent forecast cycles. Numerical simulations f...

Observations and Forecasts from the Landfall of Tropical Cyclones John, Lane, and Paul (2006) over Northwestern Mexico

AbstractThis study focuses on track and intensity changes of three tropical cyclones that, during the season of 2006, developed in the eastern North Pacific basin and made landfall over northwestern Mexico. Observational datasets, including satellite and radar imagery and a rain gauge network, are used to document regional-scale structures. Additionally, gridded fields are applied to determine the large-scale environment. John made landfall as a category-2 hurricane on the Saffir–Simpson scale and moved along the Baja California Peninsula during more than 40 h, resulting in total rainfall of up to 506 mm. The largest accumulations were located over mountains and set new records with respect to daily rates from the 1969–2005 period. Later in the season, Lane and Paul made landfall over the mainland and brought moderate rainfall over the coastal plains. Lane became a category-3 hurricane and was the third strongest hurricane to make landfall since 1969. In contrast, Paul followed a recurving track to reach ...

Development of Convective Systems over Baja California during Tropical Cyclone Linda (2003)

Abstract Characteristics of the life cycle and motion of convective systems that occurred over the Baja California Peninsula were determined from a case study in September of 2003. This note applies data from satellite imagery, regular observations from upper-air and surface networks, and operational analyses. Changes in environmental conditions over northwestern Mexico are documented and these are associated with the development of Tropical Cyclone Linda in the eastern Pacific Ocean. When Linda became a tropical storm and was located several hundred kilometers away to the southwest, a convective outbreak occurred over land. An examination of large-scale conditions indicated that flow from the eastern flank of Linda supplied low- to midlevel moisture. Significant convection is associated with specific thresholds for precipitable water, CAPE, and lifted index. Convective systems initiated in the early afternoon remained active for several hours and provided localized areas of precipitation along the wester...

Occurrence of landslides during the approach of tropical cyclone Juliette (2001) to Baja California Sur, Mexico

The approach of tropical cyclone (TC) Juliette, in 2001, to the Baja California Peninsula triggered at least 419 landslides. Most of the landslides were shallow slips and debris slides of limited areal extent, which were converted rapidly into debris flows to be exported quickly out of the mountain areas towards the lowlands. Main factors affecting landslide occurrence were total storm rainfall and intensity, aspect, geology and vegetation association. Two processes can be distinguished as initiating slope failure. Accumulation of rainfall from exposed bedrock slopes, generating excess overland flow, was the main process linked to failures in concave topography. A combination of wind and excess overland flow in the more convex or planar upper slopes was a secondary process related to heterogeneity of vegetation associations in the oak-dry tropical forests ecotone, as uprooted trees dislodged large regolith and bedrock blocks, priming hillslopes for further runoff concentration. An estimative threshold curve for triggering landslides in this region is sketched. From the analysis of historical information, storms like Juliette approach the southern peninsula on average once every 100 years. Denudation estimates are in the higher end of the spectrum for a tectonically passive margin. These estimates should be considered when taking decisions regarding management of water resources in this area through damming of streams. The results emphasize the need for a more detailed representation of the spatial distribution of the rainfall and winds for this mountainous region affected by TCs.

The Unusual Early Morning Tornado in Ciudad Acuña, Coahuila, Mexico, on 25 May 2015

AbstractThis study analyzes the synoptic- and mesoscale conditions present during initiation and intensification of the supercell thunderstorm that produced a tornado in Ciudad Acuna, a community located in the state of Coahuila, Mexico, 10 km southwest of the U.S. border. Early morning convective activity, first detected by radar at 0628 UTC 25 May 2015, developed into an intense and well-defined supercell thunderstorm that produced a tornado between approximately 1045 and 1130 UTC. Hourly analyses from the Rapid Refresh model indicated an upslope component to surface flow in the region of convection initiation over the Serranias del Burro (SdB). Along the storm’s trajectory, dewpoint temperatures increased from 15° to 22°C, convective available potential energy increased from 1500 to near 4000 J kg−1, and convective inhibition changed from −150 J kg−1 at the time of convection initiation to near zero in Ciudad Acuna. Simulations from the Weather Research and Forecasting Model confirmed the sensitivity o...