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We examined the diurnal cycle of the rainfall in a coastal tropical mountainous region in central Veracruz State, Mexico (18°–21° N, 95.5°–98.5° W), featuring a striking topographic gradient running from sea level at the Gulf of Mexico coast to 5000 m above sea level (m.a.s.l.) in less than 100 km horizontal distance. During the summer, this unique location leads to regular the interaction between the easterly moisture inflow and the mountainous barrier. Over the complex terrain, forced ascent leads the occurrence of maximum rainfall during the afternoon (16–19 local time, LT ≈ 1½ hours ahead of solar time in summer), first along the slope and later over the coast. Along the coastal plain, the precipitation continues until the early morning consistent with there being convergence between land breezes and the trade winds. Observations obtained during a measurement campaign from 28 June to 3 July 2015, indicate that during the early evening downslope winds move against easterly flow, likely due to katabatic outflows previously observed over the region. These features are confirmed using spatial (0.88°) and temporal (30 min) resolution CMORPH rainfall estimates, since we observed evening episodes initiating along the slope during the afternoon (14–17 LT) moving later towards the coast.

Herein, we present an analysis of the variability of surface air temperature at Tampico in the southern coast of Tamaulipas, northeastern Mexico, during the period 1961-2009. Several indices were used for the analysis which include the yearly highest and lowest records of maximum and minimum daily temperatures, the start and duration of the annual warm period, the temperature of the yearly warmest month, and the annual thermal oscillation. Linear trends indicate that winter temperatures are increasing (roughly 1 ∘ C decade −1 ), whereas summer temperatures have remained practically unchanged. The annual warm period starts on days 83-108 of every year and lasts 180-240 days, but there is also an apparent periodicity of 15-18 years in the occurrence of the shortest warm periods. After mid-1970s, the warm periods have decreased roughly 6 days per decade, but the temperature of the annual warmest month has increased roughly 0.50 ∘ C decade −1 , this indicates that warm periods (spring-summer) are becoming shorter but warmer. Large-scale climatic patterns also affect the low-frequency thermal variability at Tampico: the Atlantic Multidecadal Oscillation modulates the summer temperature, while El Niño variability modulates a fraction of the annual thermal oscillation via mainly delayed signals passing through the Caribbean. The higher frequency variability observed as numerous anomalous years in the temperature series may be explained mostly by dynamical factors such as a decreased southerly heat flux and/or an increased northerly heat flux (like in the year 1974), or a reduction of the annual warm period and precipitation in the northeastern Mexican coast associated with the El Niño activity (like in the year 1998). However, some cold periods may be attributable to vulcanic eruptions like those of the Chichonal (in Mexico) and the Pinatubo (in Philippines).

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