Relationships between Gulf of California Moisture Surges and Tropical Cyclones in the Eastern Pacific Basin

Abstract

Relationships between Gulf of California moisture surges and tropical cyclones (TCs) in the eastern Pacific basin are examined. Standard surface observations are used to identify gulf surge events at Yuma, Arizona, for a multiyear (July-August 1979-2001 period. The surges are related to TCs using National Hurricane Center 6-hourly track data for the eastern Pacific basin. Climate Prediction Center (CPC)-observed daily precipitation analyses and the NCEP Regional Reanalysis are used to examine the relative differences in the precipitation, atmospheric circulation, and moisture fields for several categories of surge events, including those that are directly related to TCs, indirectly related to TCs, and not related to TCs.It is shown that the response to the surge in the southwestern United States and northwestern Mexico is strongly discriminated by the presence or absence of TCs. Surges related to TCs tend to be associated with much stronger and deeper low-level southerly flow, deeper plumes of tropical moisture, and wetter conditions over the core monsoon region than surges that are unrelated to TCs. The response to the surge is also strongly influenced by the proximity of the TC to the Gulf of California (GOC) region. Tropical cyclones that track toward the GOC region exert a stronger, more direct influence on Yuma surges than those that track away from the GOC.

The Impact of Horizontal Resolution on North American Monsoon Gulf of California Moisture Surges in a Suite of Coupled Global Climate Models

“…6c,d) reveals that, in reanalyses, the most intense GoC surge-related wind anomalies occur in September ('7 vs '4 m s 21 in JulyAugust). This is most likely due to the passage of TCs south of the Baja California peninsula (Higgins and Shi 2005;Corbosiero et al 2009;Wood and Ritchie 2013). This seasonal pattern with a maximum in September is also seen in the moisture flux ('14 vs '10 m s 21 g kg 21 in…”

“…More specifically, the cyclonic anomaly that supports the development of the strong southeasterly anomalies along the Mexican and GoC coast is too broad, extends too far northward, and tends to last longer than in reanalyses. In this respect, the CM2.1 wind surges more resemble those directly associated with TCs passing close to the southern GoC (Higgins and Shi 2005).…”

“…Also evident are a concomitant progression of a TEW, or the passage of a TC (Higgins and Shi 2005;Corbosiero et al 2009;Wood and Ritchie 2013), to the south of the GoC and a midlatitude westerly disturbance over the central United States (e.g., Pascale and Bordoni 2016). In CM2.1-the model with the lowest resolutionGoC surges do not feature a realistic structure.…”

“…Over most of this region, rainfall sharply increases in June, reaching its climatological maximum in August, and decreases again in SeptemberOctober (Higgins et al 1997). The NAM-related precipitation accounts for as much as approximately 70% of the total annual rainfall in the core monsoon region of northwestern Mexico and for approximately 40% to 50% in the southwestern United States (Douglas et al 1993).…”

“…Mean and linear trends are also removed from the time series for the period 21 June-30 September, so all statistics are computed for anomalies relative to the summertime climatology. The choice of this period is justified by the fact that the monsoon onset over AZWNM typically occurs later than 21 June, while the retreat occurs more gradually in late September (Higgins et al 1997). …”