Tropical

An investigation of the vertical wind shear forcing on the intensity and track changes of Hurricane Erika has identified ten different environmental vertical wind profiles, each of which are for consecutive time periods of 12 to 45 hr, covering September 1-12, 1997. Those profiles evaluate the mean wind over a 5 degree latitude radius circle around the tropical cyclone (TC) center. Three different approaches are used. Numerical model analyses, storm center IR average images, and high density satellite winds are used. The results show that a two-level analysis of vertical shear may at times be inadequate, and that the direction of vertical shear is important to the analysis. The three methods combined with sea-surface temperature analyses, observed intensity changes, and TC motion are shown to fit a simple model approach.

A new project is planned for analysis of inner core upper winds from 1-minute visible imagery. Training and planning meetings with Kelly Findeisen (CSU graduate student), John Knaff, and Dr. William Gray’s project have taken place. This project will focus on use of SRSO manual winds in the inner core region of Hurricane Marilyn. SRSO imagery was collected on 5 consecutive days with Hurricane Marilyn (1995). Dave Watson is supporting this project with data processing and CD-ROM archiving.

Significant and interesting tropical cyclones were analyzed in near real time. Such analyses included digital IR intensity analyses, storm relative average images, and equatorial westerly wind burst analysis. The tropical cyclones were located in both Northern and Southern Hemisphere and included Hurricanes Guillermo, Linda, Nora, and Pauline in the eastern Pacific, Typhoons Ivan, Joan, Keith and Paka in the western Pacific, and Cyclones Pam, Ron and Susan in the South Pacific. Super typhoon Paka which hit Guam with considerable damage and Cyclone Pam formed as twin cyclones unusually far east in the central Pacific, in response to the ongoing strong El Nino.

High resolution (10 sec) flight (10,000 ft) level observations form the Air Force Reserve “Hurricane Hunter” C-130 reconnaissance flights for the entire 1995 season have been obtained from the Hurricane Research Division, Miami. Previously, these data have been successfully converted to MCIDAS format so that flight level information can be displayed along with the satellite imagery. In addition, programs to place these data in a storm relative position at common synoptic times (00Z, 06Z, 12Z, and 18Z) or snapshots, interpolate azimuthally around the storm in a high resolution manner, and break these data into individual radial legs have been successfully written.

Cloud track winds have been manually derived from rapid and super rapid scan images for Erika 1997, and for Luis (1995) (for only one super rapid scan period). Programs have been written to remove storm motion, and place these data in similar storm relative synoptic snapshots.

It has been shown that data from the manually derived cloud track winds derived the rapid and super rapid scan imagery, high resolution water vapor winds from the University of Wisconsin, and the radially interpolated Air Force C-130 reconnaissance can be combined to form a superior synoptic and mesoscale wind analysis around Atlantic tropical cyclones. An outline for a paper to be submitted to either Weather and Forecasting or The Journal of Atmospheric and Ocean Technology discussing this methodology has been created.

Work has begun on a case study of Hurricane Luis (1995). This study will utilize the super rapid scan satellite imagery, Air Force reconnaissance data, NCEP reanalysis data, and high resolution water vapor winds. To date individual radial legs, and azimuthally interpolated synoptic snapshots have been created using the flight level observations, and the water vapor winds and NCEP reanalysis data have been obtained from various sources.

Seasonal predictions of Atlantic tropical cyclone activity for the 1998 hurricane season (“LAD multiple linear regression forecast of Atlantic tropical cyclone activity for 1998”), and future El Nino/Southern Oscillation conditions (“Application of the El Nino - Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme”) were prepared in December and were informally published in the Climate Predictions Center’s Experimental Long-Lead Forecast Bulletin.

Two Super Typhoons occurring simultaneously in the West Pacific were studied, using GMS-5 satellite imagery. Ivan and Joan were the 8th and 9th Super Typhoons to form this year in this area of the Pacific. It was an unusual occurrence for two storms of this strength to occur at the same time and both of them being so close to satellite subpoint. Because of the close proximity to subpoint, the stadium effect (inward sloping of the eyewall), can be seen. The outflows of the two storms were unique also. Ivan's extends to the north-east while Joan's stretches to the south-west. The significance of this, is that even with their close proximity, the two outflows are not affecting one another. Daily Global Analysis SST anomaly charts, a product of NOAA/NESDIS, show that the storms produce a cold wake through upwelling. (Click on image for full size display.)