Composite structures of African easterly waves (AEWs) that develop into named tropical cyclones in the Atlantic are compared and contrasted with nondeveloping AEWs using the 40-yr ECMWF Re-Analysis (ERA-40) data and satellite brightness temperature between 1979 and 2001. Developing AEWs are characterized by a more distinctive cold-core structure two days before reaching the West African coast. As they move westward, the convective activity increases further in the vicinity of the Guinea Highlands region. At the same time the AEW trough increases its vorticity at low levels consistent with a transformation toward a more warm-core structure before it reaches the ocean. As the AEW moves over the ocean convection is maintained in the trough, consistent with the observed tropical cyclogenesis. The nondeveloping AEW has a similar evolution before reaching the coast except that the amplitudes are weaker and there is less convective activity in the Guinea Highlands region. The nondeveloping AEW composite has a more prominent dry signal just ahead of the AEW trough at mid- to upper levels. It is argued that the weaker west coast development (i.e., reduced convective activity and reduced spinup at low levels) combined with the closer proximity of the trough to mid- to upper-level dry air aloft are consistent with the nondevelopment. The most intense nondeveloping AEWs were characterized by more intense convection and stronger mid- and low-level synoptic circulations at the West African coast than the developing AEWs. The analysis strongly suggests that the lack of development was due to the presence of dry mid- to upper-level air just ahead of the AEW trough that may have been enhanced because of equatorward advection of dry air by the AEW itself.

In the wake of the eastern United States cyclone of 12-14 March 1993, a cold surge, originating over Alaska and western Canada, brought northerlies exceeding 20 m s Ϫ1 and temperature decreases up to 15ЊC over 24 h into Mexico and Central America. This paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale, focusing on 1) the structure and evolution of the leading edge of the cold surge, 2) the reasons for its extraordinary intensity and equatorward extent, and 3) the impact of the surge on the Tropics, specifically, on the strength of the trade winds and on the sea surface temperature in the eastern Pacific. The cold surge was initiated as a developing cyclone over the Gulf of Mexico, and an upstream anticyclone east of the Rockies caused an along-barrier pressure gradient to form, forcing topographically channeled northerlies along the Rocky and Sierra Madre Mountains to transport cold air equatorward. On the mesoscale, the leading edge of the cold surge possessed nonclassical frontal structure. For example, as the cold surge entered Mexico, the coldest air and the strongest wind arrived at about 900 hPa before affecting the surface, suggestive of a tipped-forward leading edge to the surge. Also, satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air. The cold surge had characteristics reminiscent of a Kelvin wave, a tipped-forward cold front, a pressure-jump line, a bore, and a gravity current, but none of these conceptual/dynamical models was fully applicable. Associated with the cold surge, gap winds up to 25 m s Ϫ1 were observed in the Gulfs of Tehuantepec (a tehuantepecer), Fonseca, Papagayo, and Panama, owing to the strong cross-mountain pressure gradient. In the case of the tehuantepecer, a rope cloud emanated from the Isthmus of Tehuantepec and turned anticyclonically, consistent with an inertial oscillation. On the synoptic and planetary scales, the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold-air damming, by a low-latitude upper-tropospheric trough, and by the lower branch of the secondary circulation associated with a confluent jet-entrance region aloft. The cold surge also impacted the tropical atmosphere and ocean, by contributing to the strengthening of the northeast trade winds over the eastern Pacific Ocean and by inducing local cooling of the sea surface temperature in the Gulfs of Tehuantepec and Papagayo by about 4Њ-8ЊC.

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The Eighth Cyclone Workshop was held at the Far Hills Inn and Conference Center in Val Morin, Quebec, Canada, 12-16 October 1992. The workshop was arranged around several scientific themes of current research interest. The most widely debated theme was the applicability of "potential vorticity thinking" to theoretical, observational, and numerical studies of the life cycle of cyclones and the interaction of these cyclones with their environment on all spatial and temporal scales. A combination of invited and contributed talks, with preference given to younger scientists, made up the workshop. 1. Workshop background Working scientists and students interested in cyclone-related research problems have used the venue of periodic cyclone workshops to exchange ideas and information from observational, theoretical, and numerical studies of cyclogenesis and the life cycle of cyclones. This article reports on the most recent cyclone workshop gathering, held at the

Florida annually leads the nation in lightning-caused fatalities. While many studies have examined the lightning frequency maximum near Cape Canaveral, relatively little attention has been paid to the western Florida peninsula, which features a similar warm-season lightning event density. Of particular concern are first cloud-to-ground (FCG) lightning events in developing thunderstorms, which are difficult to predict with sufficient lead time and can catch people off-guard. This study performs an environmental analysis of warm-season (May–September) FCG events (2014–2021) across the western Florida peninsula using high-resolution model analysis data, including a comparison to null (No CG) days. FCG events and No CG days are first identified from ground-based lightning data and partitioned into nine synoptic-scale flow regimes. Next, spatiotemporal distributions of FCG events are elucidated for the western Florida peninsula. An ingredients-based analysis shows that the convective environment one hour before FCG events during strong south-southeast flow features the largest amounts of moisture, but smallest instability values and weak mid-tropospheric lapse rates, primarily due to warm advection and moisture transport from the Atlantic Ocean. Environments one hour before FCG events in all nine flow regimes feature markedly greater instability values, larger relative humidity values, and steeper mid-tropospheric lapse rates than do No CG days. Results emphasize that instability and moisture are the key ingredients for warm-season FCG events in the region. Convective parameter statistical distributions and composite soundings populate an online dashboard that can be used by regional forecasters to better predict FCG events and increase alert lead times.

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