4 Comparison of Halloween 

 Storm with ERICA IOP-4 

 Event 



26 



The January 1989 event examined by Neiman and Shapiro (1993) is 

 described by them as one of the most intense cases of extratropical marine 

 cyclone development observed in the western Atlantic geographical region. 

 The IOP-4 event analyzed by Neiman and Shapiro (1993) is the same cited by 

 Pauley and Bramer (1992) and referred to in the previous section of this 

 report. The 850-mb temperature contrast for that event was approximately 

 28 °C (+08 °C to -20 °C). The 850-mb temperature contrast for the Hallow- 

 een Storm was comparable at 25 °C (+15 °C to -10 °Q. The Halloween 

 Storm did not intensify as rapidly as did the IOP-4 event, which deepened at 

 least 60 mb in 24 hr and attained a minimum sea-level pressure of 936 mb and 

 a pressure deficit of at least 80 mb (Nieman, Shapiro, and Fedor 1993). The 

 Halloween Storm deepened only about 40 mb in 48 hr, far less than the IOP-4 

 event. However, the Halloween Storm eventually attained a maximum pres- 

 sure deficit of 70 mb (NO A A 1992), comparable to that of the IOP-4 event 

 Moreover, the duration of the Halloween Stomi was at least twice as great as 

 that of the IOP-4 event 



While the peak winds of both events were comparable (25 m/s), the coastal 

 impact of the IOP-4 event was not significant because of the short duration 

 and because the track resulted in alongshore or offshore wind directions along 

 most reaches of the northern U.S. coastline. At the time of peak storm inten- 

 sity, the onshore wind directions were confined mostly to coastal Newfound- 

 land. The Halloween Storm is compared to the IOP-4 event because the 

 events are similar and IOP-4 is certainly the best-documented event to occur in 

 a similar geographic regioru Even so, there are significant differences, particu- 

 larly with regard to the presence of Hurricane Grace during the formative 

 stages of the Halloween Storm. Perhaps an objective way to view the influ- 

 ence of Hurricane Grace is not as system-system interaction, but to examine 

 the roles of the strong pressure and temperature gradients in the formation of 

 the Halloween Storm. 



Chapter 4 Comparison of Halloween Storm with ERICA IOP-4 Event 



