Post by ndg on Jul 31, 2014 15:01:14 GMT -6
If you are wondering why the CSU forecast is still calling for slower than normal rest of the hurricane season despite a neutral ENSO remaining and a much weaker forecasted El Nino, here is why:
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As was the case last year, the tropical Atlantic is much drier than normal this year. While there are issues with the NCEP/NCAR Reanalysis mid-level moisture estimates, it is likely that July 2014 is one of the driest Julys on record. The NCEP/NCAR Reanalysis reports that MDR 600-mb relative humidity in July 2014 is the driest on record by a large margin.
Figure 14: July 2014 600-mb relative humidity anomalies across the tropical Atlantic. Very dry conditions have been observed across the entire region.
According to AOML’s Jason Dunion (personal communication), African dust outbreaks have been quite strong this year as well. The Cooperative Research Institute for the Atmosphere (CIRA) monitors real-time conditions for genesis in the tropical Atlantic, and according to their analysis, vertical instability is significantly below normal this year (Figure 15). Positive deviations from the curve displayed below indicate a more unstable atmosphere than normal. In general, the atmosphere has been much more stable than normal since the start of the hurricane season.
Figure 15: Vertical instability across the tropical Atlantic since January 2014 (blue line). The average season is represented by the black line.
Table 8 summarizes conditions across both the MDR and Caribbean (10-20°N, 90-60°W) for July 2014 in standardized anomaly form from the 1981-2010 average. Several parameters are displayed in the table (including SST, SLP, 850-mb zonal wind, 200-mb zonal wind, 200-850-mb zonal wind shear and 600-mb relative humidity). Note that most parameter deviations in July 2014 are considered unfavorable for hurricane formation/intensification.
Figure 14: July 2014 600-mb relative humidity anomalies across the tropical Atlantic. Very dry conditions have been observed across the entire region.
According to AOML’s Jason Dunion (personal communication), African dust outbreaks have been quite strong this year as well. The Cooperative Research Institute for the Atmosphere (CIRA) monitors real-time conditions for genesis in the tropical Atlantic, and according to their analysis, vertical instability is significantly below normal this year (Figure 15). Positive deviations from the curve displayed below indicate a more unstable atmosphere than normal. In general, the atmosphere has been much more stable than normal since the start of the hurricane season.
Figure 15: Vertical instability across the tropical Atlantic since January 2014 (blue line). The average season is represented by the black line.
Table 8 summarizes conditions across both the MDR and Caribbean (10-20°N, 90-60°W) for July 2014 in standardized anomaly form from the 1981-2010 average. Several parameters are displayed in the table (including SST, SLP, 850-mb zonal wind, 200-mb zonal wind, 200-850-mb zonal wind shear and 600-mb relative humidity). Note that most parameter deviations in July 2014 are considered unfavorable for hurricane formation/intensification.