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1998 and 1999, when waves triggered 86% and 91% of the named storms, respectively. These two seasons were characterized by a larger number of intense hurricanes originating from waves in the deep Tropics at a time when low shear and an unstable environment prevailed. In 1997, on the other hand, even though the waves were not significantly different in structure, the wind shear was high over the deep Tropics and the contribution from waves to tropical cyclones was only 28%. 4. Forecast verifications
1998 and 1999, when waves triggered 86% and 91% of the named storms, respectively. These two seasons were characterized by a larger number of intense hurricanes originating from waves in the deep Tropics at a time when low shear and an unstable environment prevailed. In 1997, on the other hand, even though the waves were not significantly different in structure, the wind shear was high over the deep Tropics and the contribution from waves to tropical cyclones was only 28%. 4. Forecast verifications
Abstract
The 1997 Atlantic hurricane season is summarized and the year’s tropical storms, hurricanes, and one subtropical storm are described. The tropical cyclones were relatively few in number, short lived, and weak compared to long-term climatology. Most systems originated outside the deep Tropics. Hurricane Danny was the only system to make landfall. It produced rainfall totals to near 1 m in southern Alabama and is blamed for five deaths. Hurricane Erika was responsible for the season’s two other fatalities, in the coastal waters of Puerto Rico.
Abstract
The 1997 Atlantic hurricane season is summarized and the year’s tropical storms, hurricanes, and one subtropical storm are described. The tropical cyclones were relatively few in number, short lived, and weak compared to long-term climatology. Most systems originated outside the deep Tropics. Hurricane Danny was the only system to make landfall. It produced rainfall totals to near 1 m in southern Alabama and is blamed for five deaths. Hurricane Erika was responsible for the season’s two other fatalities, in the coastal waters of Puerto Rico.
Africansystems observed since our annuat summary began in 1968. African seedlings initiated four of the eightnamed Atlantic storms, and all but one of the fourteen East Pacific storms.1. Introduction This is the ninth consecutive year a seasonal tropicaldisturbance summary has been completed. The generalphilosophy of the counting method was outlined inprevious articles by Simpson et al. (1968, 1969). Last year Hebert (1976) speculated the tropics maybe .returning to normal, and this trend continued
Africansystems observed since our annuat summary began in 1968. African seedlings initiated four of the eightnamed Atlantic storms, and all but one of the fourteen East Pacific storms.1. Introduction This is the ninth consecutive year a seasonal tropicaldisturbance summary has been completed. The generalphilosophy of the counting method was outlined inprevious articles by Simpson et al. (1968, 1969). Last year Hebert (1976) speculated the tropics maybe .returning to normal, and this trend continued
-level low. Martin (1975)found that the lifetime of most cloud clusters in theITCZ was generally less than 24 to 36 hours. In ourcounting scheme, we do not include ITCZ disturbancesunless their cloud clusters persist for at least 48 h. Thismeans that we probably identify only the strongerITCZ disturbances, but this is consistent with ourdesire to only document synoptic features whose timescale is days. Hebert (1976) speculates that the tropics may bereturning to normal. Residents within the
-level low. Martin (1975)found that the lifetime of most cloud clusters in theITCZ was generally less than 24 to 36 hours. In ourcounting scheme, we do not include ITCZ disturbancesunless their cloud clusters persist for at least 48 h. Thismeans that we probably identify only the strongerITCZ disturbances, but this is consistent with ourdesire to only document synoptic features whose timescale is days. Hebert (1976) speculates that the tropics may bereturning to normal. Residents within the
high pressure to its south produced easterly low-level winds across the deep Tropics of the western North Pacific. Within these low-latitude easterly winds, several tropical disturbances formed. The tropical disturbance that became Typhoon Niki (18W) can be traced to a small cluster of MCSs, which appeared in the eastern Caroline Islands on 13 August. This disturbance moved westward and developed slowly. It became a tropical storm after it crossed 130°E and before it crossed Luzon. Niki did not
high pressure to its south produced easterly low-level winds across the deep Tropics of the western North Pacific. Within these low-latitude easterly winds, several tropical disturbances formed. The tropical disturbance that became Typhoon Niki (18W) can be traced to a small cluster of MCSs, which appeared in the eastern Caroline Islands on 13 August. This disturbance moved westward and developed slowly. It became a tropical storm after it crossed 130°E and before it crossed Luzon. Niki did not
trough and abundant deep convection, the number of TCs of at least tropical storm intensity was near normal. The TCs of 1997 tended to emerge one by one from the eastern portion of the basin and then recurve or move north, with each subsequent development at low latitude tending to occur after the prior TC had exited the Tropics. Many of the TCs were large, very intense, and slow moving. There were relatively few cases of multiple TCs (i.e., the simultaneous occurrence of two or more) in the WNP
trough and abundant deep convection, the number of TCs of at least tropical storm intensity was near normal. The TCs of 1997 tended to emerge one by one from the eastern portion of the basin and then recurve or move north, with each subsequent development at low latitude tending to occur after the prior TC had exited the Tropics. Many of the TCs were large, very intense, and slow moving. There were relatively few cases of multiple TCs (i.e., the simultaneous occurrence of two or more) in the WNP
Tropics of the Pacific basin, the U.S. Climate Prediction Center (along with other international meteorological centers) declared that the warm phase of ENSO was over. In some respects (e.g., the cooling of the equatorial sea surface, and the anomalously strong low-level easterly winds in the low latitudes of the WNP), the climatic anomalies of the Pacific basin during most of 1995 were consistent with those expected during a cold phase of ENSO, sometimes referred to as La Niña or El Viejo
Tropics of the Pacific basin, the U.S. Climate Prediction Center (along with other international meteorological centers) declared that the warm phase of ENSO was over. In some respects (e.g., the cooling of the equatorial sea surface, and the anomalously strong low-level easterly winds in the low latitudes of the WNP), the climatic anomalies of the Pacific basin during most of 1995 were consistent with those expected during a cold phase of ENSO, sometimes referred to as La Niña or El Viejo
( Simpson et al. 1969 ; Avila and Guiney 2000 ). An increase in the number of Atlantic storms could potentially decrease the vigor of waves crossing into the Pacific. Atlantic Hurricanes Cindy, Dennis, Floyd, Gert, and Jose all formed from tropical waves and then moved out of the Tropics. While tropical waves spawn more than one TC occasionally, the remnant wave vorticity after genesis often appears greatly reduced. A pattern of above-normal activity in the Atlantic coupled with below-normal activity
( Simpson et al. 1969 ; Avila and Guiney 2000 ). An increase in the number of Atlantic storms could potentially decrease the vigor of waves crossing into the Pacific. Atlantic Hurricanes Cindy, Dennis, Floyd, Gert, and Jose all formed from tropical waves and then moved out of the Tropics. While tropical waves spawn more than one TC occasionally, the remnant wave vorticity after genesis often appears greatly reduced. A pattern of above-normal activity in the Atlantic coupled with below-normal activity
season of 1997. Mon. Wea. Rev. , 127 , 2440 – 2454 . Madden , R. A. , and P. R. Julian , 1972 : Description of global-scale circulation cells in the Tropics with a 40–50 day period. J. Atmos. Sci. , 29 , 1109 – 1123 . Neumann , C. B. , 1972 : An alternate to the HURRAN (hurricane analog) tropical cyclone forecast system. NOAA Tech. Memo. NWS SR-62, 24 pp . NWS , 2006 : National Weather Service (NWS) Manual 10-604: Tropical cyclone definitions. 9 pp. [Available online at http
season of 1997. Mon. Wea. Rev. , 127 , 2440 – 2454 . Madden , R. A. , and P. R. Julian , 1972 : Description of global-scale circulation cells in the Tropics with a 40–50 day period. J. Atmos. Sci. , 29 , 1109 – 1123 . Neumann , C. B. , 1972 : An alternate to the HURRAN (hurricane analog) tropical cyclone forecast system. NOAA Tech. Memo. NWS SR-62, 24 pp . NWS , 2006 : National Weather Service (NWS) Manual 10-604: Tropical cyclone definitions. 9 pp. [Available online at http
in the tropics with 40-50 day period. J. Atmos. Sci. , 29 , 1109 – 1123 . Neumann , C. B. , 1972 : An alternate to the HURRAN (hurricane analog) tropical cyclone forecast system. NOAA Tech. Memo. NWS SR-62, 24 pp . Saffir , H. S. , 1973 : Hurricane wind and storm surge. Mil. Eng. , 423 , 4 – 5 . Simpson , R. H. , 1974 : The hurricane disaster potential scale. Weatherwise , 27 , 169 – 186 . Fig . 1. (a) Track chart of the first nine eastern North Pacific tropical storms and
in the tropics with 40-50 day period. J. Atmos. Sci. , 29 , 1109 – 1123 . Neumann , C. B. , 1972 : An alternate to the HURRAN (hurricane analog) tropical cyclone forecast system. NOAA Tech. Memo. NWS SR-62, 24 pp . Saffir , H. S. , 1973 : Hurricane wind and storm surge. Mil. Eng. , 423 , 4 – 5 . Simpson , R. H. , 1974 : The hurricane disaster potential scale. Weatherwise , 27 , 169 – 186 . Fig . 1. (a) Track chart of the first nine eastern North Pacific tropical storms and
