Search Results

You are looking at 1 - 10 of 14 items for :

  • Author or Editor: Steven Businger x
  • Weather and Forecasting x
  • Refine by Access: Content accessible to me x
Clear All Modify Search
Steven J. Caruso and Steven Businger

Abstract

The occurrence of subtropical cyclones over the central North Pacific Ocean has a significant impact on Hawaii’s weather and climate. In this study, 70 upper-level lows that formed during the period 1980–2002 are documented. In each case the low became cut off from the polar westerlies south of 30°N over the central Pacific, during the Hawaiian cool season (October–April). The objectives of this research are to document the interannual variability in the occurrence of upper-level lows, to chart the locations of their genesis and their tracks, and to investigate the physical mechanisms important in associated surface development. Significant interannual variability in the occurrence of upper-level lows was found, with evidence suggesting the influence of strong El Niño–Southern Oscillation events on the frequency of subtropical cyclogenesis in this region. Of the 70 upper-level lows, 43 were accompanied by surface cyclogenesis and classified as kona lows. Kona low formation is concentrated to the west-northwest of Hawaii, especially during October and November, whereas lows without surface development are concentrated in the area to the east-northeast of Hawaii. Kona low genesis shifts eastward through the cool season, favoring the area to the east-northeast of Hawaii during February and March, consistent with a shift in the climatological position of the trough aloft during the cool season. Consistent with earlier studies, surface deepening is well correlated with positive vorticity advection by the thermal wind. Static stability and advection of low-level moisture are less well correlated to surface deepening. These results suggest that kona low formation, to first order, is a baroclinic instability that originates in the midlatitudes, and that convection and latent-heat release play a secondary role in surface cyclogenesis.

Full access
Ian Morrison and Steven Businger

Abstract

A subtropical cyclone or kona low affected the island of Hawaii on 24–28 February 1997 and brought with it record winds at Hilo, large hail, blizzard conditions at higher elevations, and high surf. Damage estimates for the storm due to crop loss, property damage, and utility line destruction exceed $4 million. A detailed case study of the storm was conducted using all available operational data and data from the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset. The kona low formed on 23 February 1997 along a stalled trough northeast of the Hawaiian Islands and is investigated during five evolutionary stages: (i) incipient, (ii) intensifying, (iii) mature, (iv) weakening, and (v) dissipating.

The system’s initial development is linked to dynamics at the 250-mb level. The maximum circulation, absolute vorticity, divergence, and height anomalies all occurred at 250 mb during the period of most rapid deepening. Cold anomalies occurred in a deep layer between 850 and 250 mb that tilted eastward with height. Quasigeostrophic analysis showed enhanced vorticity to the west of a thickness trough, a configuration that maintained an area of positive vorticity advection to the west of the surface low and over new convection east and southeast of the low. The vorticity tendency is dominated by the advection of vorticity aloft in this case, especially during the incipient and intensifying stages. The vorticity tendency is dominated by the generation of vorticity by divergence in the lower troposphere.

Cloud bands with embedded convective cells formed on the low’s eastern side and propagated eastward, eventually leaving the area of synoptic-scale ascent and losing their convective properties. Areas where the best-lifted index values were less than zero and areas of positive low-level advection of equivalent potential temperature coincided with regions of deep convection, as inferred from satellite imagery.

Full access
Steven Businger and Richard J. Reed

Abstract

The small-scale and rapid development of polar lows over relatively data-sparse areas results in a special forecast challenge for the operational forecasting community. This paper constitutes a review of recent advances in our understanding of cyclogenesis in polar air masses. The review is primarily comprised of a survey of the observed features of polar lows as documented in a number of case studies presented in the recent literature. The review is organized on the basis of a combination of observational and physical considerations and is aimed at diagnosing common types of developments. Theoretical ideas concerning the origins of polar lows and results of numerical modeling experiments aimed at simulating their development are also summarized. Finally, a discussion of approaches to the operational problem of forecasting polar lows is given.

Full access
Kevin R. Kodama and Steven Businger

Abstract

The large area of responsibility covered by the Pacific Region of the National Weather Service provides a unique set of challenges to operational forecasters. Extratropical, subtropical, and tropical meteorological phenomena on a wide range of temporal and spatial scales must be considered on a daily basis. Compounding the problems of forecasting diverse weather for such a large area of responsibility is the fact that the Pacific Ocean is a data-sparse region. Recent improvements in data collection platforms and the continued progress made by researchers have helped increase the understanding of weather throughout the region, ultimately resulting in improved forecast services.

This article provides an overview of some of the weather phenomena encountered in the Pacific Region and helps set the stage for the accompanying articles that focus on specific weather forecasting problems. Some discussion is provided on the impact of the National Weather Service’s modernization program on operational forecasting in the region.

Full access
Thomas E. Robinson and Steven Businger

Abstract

A new method for modeling the lowest model level vertical motion is described and validated. Instead of smoothing terrain heights, the new method calculates the terrain gradient on a high-resolution grid and averages the gradient values around a gridpoint location. In essence, the method provides a way to achieve some of the impact of very steep terrain on the flow without the computational overhead associated with the very high grid resolution needed to fully resolve complex terrain. The more accurate depiction of the terrain gradient leads to an increase in orographic vertical motion and causes rainfall to occur more often over the windward-facing mountain slopes, consistent with observations. Model results are compared with rain gauge data during the month of January 2016 as well as radar data from a case study on 9 March 2012. When implemented in the Weather Research and Forecasting (WRF) Model over the island of Oahu and compared with the current WRF method, the model precipitation forecast skill is improved. The new method produces more precipitation over the island during January 2016, which is closer to the observed value. On 9 March 2012, the new method clearly focuses the precipitation over the Ko‘olau Mountains, reducing the number of false alarm forecasts by nearly one-half. Although the changes to model precipitation skill were small, they were generally positive.

Full access
Steven Businger, Selen Yildiz, and Thomas E. Robinson

Abstract

This study analyzes QuikSCAT surface wind data over the North Pacific Ocean to document the distribution of captured fetches in extratropical cyclones that produced hurricane force (HF) wind fields from January 2003 through May 2008. A case study is presented to introduce the datasets, which include surface wind analyses from the Global Forecast System (GFS) Global Data Assimilation System (GDAS), and wave hindcasts from the third-generation wave model (WAVEWATCH III; hereafter, WW3), in addition to the QuikSCAT surface wind data. The analysis shows significant interannual variability in the location of the captured fetches as documented by QuikSCAT, including a shift in the distribution of captured fetches associated with ENSO. GDAS surface winds over the ocean are consistently underanalyzed when compared to QuikSCAT surface winds, despite the fact that satellite observations of ocean surface winds are assimilated. When the WW3 hindcasts associated with HF cyclones are compared with buoy observations over the eastern and central North Pacific Ocean, the wave model significantly underestimates the large-swell events.

Full access
Steven Businger, David I. Knapp, and Gerald F. Watson

Abstract

A storm-following climatology was compiled for the precipitation distributions associated with winter cyclones that originate over the Gulf of Mexico and adjacent coastal region. The goal of this research is to investigate the roles of the Gulf of Mexico and Atlantic Ocean as sources of moisture for these storms, and to investigate geographic/orographic influences on the precipitation distributions. A second objective of this research is to provide forecasters with a potential guide with which to evaluate numerical model forecasts of quantitative precipitation for these storms. A 24-y climatology (1960–1983) was compiled of storms that originated over the Gulf of Mexico and adjacent coastal region, and produced wide-spread areas of precipitation (total ≥ 25 mm). Sixty-six storms satisfied these criteria, and three dominant storm tracks were identified. Six-h totals of hourly precipitation data were objectively analysed for individual storm belonging to each of the three tracks, and grid-point values were composited in a storm-following coordinate system. Charts of mean precipitation distributions and frequency of occurrence were constructed to display the evolving precipitation fields surrounding storms belonging to each track. The resulting climatology is presented.

To provide an example of the application of the precipitation climatology, results from a GALE Case study am presented.

Full access
William H. Bauman III, Michael L. Kaplan, and Steven Businger

Abstract

Space shuttle landings at the shuttle landing facility at Kennedy Space Center are subject to strict weather-related launch commit criteria and flight rules. Complex launch commit criteria and end-of-mission flight rules demand very accurate nowcasts (forecasts of less than 2 h) of cloud, wind, visibility, precipitation, turbulence, and thunderstorms prior to shuttle launches and landings.

During easterly flow regimes the onset of convective activity has proven to be particularly difficult to predict. Contrasting weather ranging from clear skies to thunderstorms occurs on days with seemingly similar synoptic environments. Four days of easterly flow during the Convection and Precipitation/Electrification (CaPE) Experiment were investigated in an effort to identify and simulate key features that distinguish convectively active and suppressed conditions. Data from CaPE and operational data, including satellite imagery and National Centers for Environmental Prediction model analysis output over the Florida peninsula and surrounding data-sparse Atlantic Ocean, are combined in the research. It is found that elevated moisture in the midtroposphere above the marine boundary layer helps distinguish convectively active and passive days. Moreover, analysis reveals that the moisture distribution is related to jet dynamics in the upper troposphere.

A series of simulations using the Mesoscale Atmospheric Simulation System (MASS) model was undertaken. The MASS model run with a coarse grid (45 km) correctly simulates the development of the upper-level jet streak and its general impact on convective activity over the Florida peninsula. The MASS model run with a nested (11 km) grid and moisture enhancement of the initial model state from radar, satellite, and surface data results in the best short-term (6 h) forecast of relative humidity and precipitation patterns over the Florida peninsula and proximate coastal environment. Implications of the research results for nowcasting convective activity over Cape Canaveral are discussed.

Full access
Robert A. Mazany, Steven Businger, Seth I. Gutman, and William Roeder

Abstract

The primary weather forecast challenge at the Cape Canaveral Air Station and Kennedy Space Center is lightning. This paper describes a statistical approach that combines integrated precipitable water vapor (IPWV) data from a global positioning system (GPS) receiver site located at the Kennedy Space Center (KSC) with other meteorological data to develop a new GPS lightning index. The goal of this effort is to increase the forecasting skill and lead time for prediction of a first strike at the KSC. Statistical regression methods are used to identify predictors that contribute skill in forecasting a lightning event. Four predictors were identified out of a field of 23 predictors that were tested, determined using data from the 1999 summer thunderstorm season. They are maximum electric field mill values, GPS IPWV, 9-h change in IPWV, and K index. The GPS lightning index is a binary logistic regression model made up of coefficients multiplying the four predictors. When time series of the GPS lightning index are plotted, a common pattern emerges several hours prior to a lightning event. Whenever the GPS lightning index falls to 0.7 or below, lightning occurs within the next 12.5 h. An index threshold value of 0.7 was determined from the data for lightning prediction. Forecasting time constraints based on KSC weather notification requirements were incorporated into the verification. Forecast verification results obtained by using a contingency table revealed a 26.2% decrease from the KSC's previous-season false alarm rates for a nonindependent period and a 13.2% decrease in false alarm rates for an independent test season using the GPS lightning index. In addition, the index improved the KSC desired lead time by nearly 10%. Although the lightning strike window of 12 h is long, the GPS lightning index provides useful guidance to the forecaster in preparing lighting forecasts, when combined with other resources such as radar and satellite data. Future testing of the GPS lightning index and the prospect of using the logistic regression approach in forecasting related weather hazards are discussed.

Full access
Lacey Holland, Steven Businger, Tamar Elias, and Tiziana Cherubini

Abstract

Kīlauea volcano, located on the island of Hawaii, is one of the most active volcanoes in the world. It was in a state of nearly continuous eruption from 1983 to 2018 with copious emissions of sulfur dioxide (SO2) that affected public health, agriculture, and infrastructure over large portions of the island. Since 2010, the University of Hawaiʻi at Mānoa provides publicly available vog forecasts that began in 2010 to aid in the mitigation of volcanic smog (or “vog”) as a hazard. In September 2017, the forecast system began to produce operational ensemble forecasts. The months that preceded Kīlauea’s historic lower east rift zone eruption of 2018 provide an opportunity to evaluate the newly implemented air quality ensemble prediction system and compare it another approach to the generation of ensemble members. One of the two approaches generates perturbations in the wind field while the other perturbs the sulfur dioxide (SO2) emission rate from the volcano. This comparison has implications for the limits of forecast predictability under the particularly dynamic conditions at Kīlauea volcano. We show that for ensemble forecasts of SO2 generated under these conditions, the uncertainty associated with the SO2 emission rate approaches that of the uncertainty in the wind field. However, the inclusion of a fluctuating SO2 emission rate has the potential to improve the prediction of the changes in air quality downwind of the volcano with suitable postprocessing.

Restricted access