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José Fernández-Partagás
and
Henry F. Diaz

A historical revision of Atlantic tropical cyclones for the period 1851–90 is presented. This work was undertaken with the aim of improving knowledge of the tropical storms and hurricanes in the North Atlantic basin, which occurred during the latter half of the nineteenth century. Another aim of the study was to develop more reliable figures regarding cyclone frequency variations than those that were currently available. The 40-yr period covered by this study spans the 20 yr (1851–70) prior to the founding of a U.S. meteorological service as part of the U.S. Signal Service and the approximately 20 yr (1871–90) that military personnel of that service took care of the official meteorological affairs in the country, prior to the establishment of a civilian U.S. Weather Bureau within the U.S. Department of Agriculture. The period 1851–90 was found to be particularly attractive from a research standpoint because it covered the time elapsed from 1855, the last year included in the storm catalog prepared by Poey, which is used in the cyclone list shown by Tannehill, to 1878, the year the Signal Service began to systematically trace all West Indian hurricanes.

A comparison of hurricane activity, in terms of the total number of storms, is made between the 40-yr period of 1851–90, and the corresponding period in the twentieth century. Even after taking into account the large differences in the observational network during these two periods, a century apart, there is some suggestion that the earlier period was relatively less active.

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Jose Fernandez-Partagas
and
Christopher N. K. Mooers

Abstract

Kinematic aspects of winter cold fronts in Florida are examined for a subsynoptic scale representing the frontal wind shift at the earth's surface. Fifteen selected cold fronts are studied by using time series of surface wind observations for Miami, Fla. With the aid of frontal movements estimated from six-hourly synoptic charts, the spatial wind distribution near the frontal wind shift is obtained by transforming time series observations into space series. The study of steady wind regimes ahead and behind the front indicates that the major wind change across the front occurs only in the v-component. As measured along a direction perpendicular to the front (136°T), this major change occurs over a distance of about 140 km, corresponding to a time scale of about 4.5 h. Divergence and vorticity estimates are based upon the subsynoptic wind distribution. These estimates are similar to those found previously for non-frontal subsynoptic studies on moist convection in Florida. It is found that our estimates can be roughly approximated by the spatial derivative of the v-component.

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Jose J. Fernandez-Partagas
and
Mariano A. Estoque

Abstract

Relationships between convergence and rainfall at subsynoptic scales of motion are studied observationally. Data are based on special surface wind and rainfall observations in the South Florida peninsula during the period 11–13 July 1971. It is shown that larger scale convergence produces smaller scale convergence which, in turn, induces rainfall. The convective rainfall lags behind the large (peninsular) scale convergence by approximately 2 hr. In addition, the smaller scale divergence associated with rainfall produces larger scale divergence. The importance of the results in relation to parameterization and short-range forecasting of convective rainfall is discussed.

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Luis M. Herrera Cantilo
and
Jose J. Fernandez-Partagas

Abstract

A tropical depression approached the Lesser Antilles on 26 July 1969 and remained under radar surveillance for more than 12 hr. Radar echoes observed from Barbados were tracked and used to define a motion field. This motion field was compared to winds observed by instrumented aircraft. Echoes were found to move to the left of the wind directions reported at 1500 m and faster than the winds measured at 3000 m.

The field of motion derived from the radar echoes, which is not the wind field, was analyzed in terms of vorticity and divergence. These quantities were found to be correlated as expected, and different centers of maximum vorticity dominated the field throughout the duration of the study. A process of reformation toward the north was observed after 1400 GMT.

In an experiment with the tendency equation for absolute vorticity as applied to the field of motion inferred from the echoes, the local time derivative, the horizontal advection and the divergence term were computed directly. All other terms were lumped into a residual. This residual was found to be as large as the first two terms, while the divergence term was consistently smaller. However, large values of the divergence term were found in areas of maximum vorticity. Large values of the residual, on the other hand, appear to be related to areas of intense convection.

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THOMAS H. CARPENTER
,
RONALD L. HOLLE
, and
JOSE J. FERNANDEZ-PARTAGAS

Abstract

To examine the hypothesis of a worldwide relation between some lunar periods and tropical disturbances, we collected first-formation dates for 1,013 hurricanes and typhoons and 2,418 tropical storms in both hemispheres. Using the superposed epoch method, we found a lunar synodic cycle (29.53 days) in North Atlantic hurricane and northwest Pacific typhoon formation dates. About 20 percent more hurricanes and typhoons formed near new and full moon than near the quarters during a 78-yr period, showing a stronger peak at new moon than at full moon. Statistically, the existence of an effect dependent on the lunar synodic cycle is supported by a significance level of 7 percent on unsmoothed data from an analysis of variance for categorical data.

During the same 78 yr. North Atlantic tropical storms that did not later become hurricanes tended to form near the lunar quarters. Several other categories of tropical storms were not clearly related to the synodic month. Severe tropical storms in two portions of the Indian Ocean over 75 yr formed more often several days after syzygy and quadrature, but this and other severe tropical storm results lack definition, probably due to poor data.

Theoretical calculations of the lunar-solar gravitational tide showed that the anomalistic lunar cycle affects only the amplitude and not the timing of extrema. No marked anomalistic or latitude components in hurricane formation were found.

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