Philip J. Klotzbach

On the Madden-Julian Oscillation-Atlantic Hurricane Relationship

Abstract The large-scale equatorial circulation known as the Madden–Julian oscillation (MJO) has been shown to impact tropical cyclone activity in several basins around the globe. In this paper, the author utilizes an MJO index created by Wheeler and Hendon to examine its impacts on tropical genesis and intensification in the Atlantic. Large differences in frequency and intensity of tropical cyclone activity are seen, both in the tropical Atlantic as well as in the northwest Caribbean and Gulf of Mexico depending on the MJO phase. Coherent changes in upper- and lower-level winds and relative humidity are likely responsible for these differences. Since the MJO shows potential predictability out to about two weeks, the relationships discussed in this paper may be useful for short-term predictions of the probability of tropical cyclone activity in the Atlantic as a complement to the already available longer-term seasonal predictions.

Multidecadal Variability in North Atlantic Tropical Cyclone Activity

Abstract Recent increases in Atlantic basin tropical cyclone activity since 1995 and the associated destructive U.S. landfall events in 2004 and 2005 have generated considerable interest into why there has been such a sharp upturn. Natural variability, human-induced global warming, or a combination of both factors, have been suggested. Several previous studies have discussed observed multidecadal variability in the North Atlantic over 25–40-yr time scales. This study, using data from 1878 to the present, creates a metric based on far North Atlantic sea surface temperature anomalies and basinwide North Atlantic sea level pressure anomalies that shows remarkable agreement with observed multidecadal variability in both Atlantic basin tropical cyclone activity and in U.S. landfall frequency.

Updated 6–11-Month Prediction of Atlantic Basin Seasonal Hurricane Activity

Abstract An updated statistical scheme for forecasting seasonal tropical cyclone activity in the Atlantic basin by 1 December of the previous year is presented. Previous research by Gray and colleagues at Colorado State University showed that a statistical forecast issued on 1 December of the previous year could explain up to about 50% of the jackknife hindcast variance for the 1950–90 time period. Predictors utilized in the original forecast scheme included a forward extrapolation of the quasi-biennial oscillation (QBO) and two measures of West African rainfall. This forecast has been issued since 1991 but has shown little skill because of the as yet unexplained failure of the West African rainfall predictors during the 1990s. The updated scheme presented in this paper does not utilize West African rainfall predictors. It employs the new NCEP–NCAR reanalysis data and involves predictors that span the globe. Much experimentation has led to the choosing of conditions associated with the El Nino-Southern Os...

Revised Prediction of Seasonal Atlantic Basin Tropical Cyclone Activity from 1 August

Predictions of the remainder of the season’s Atlantic basin tropical cyclone activity from 1 August have been issued by Gray and his colleagues at the Tropical Meteorology Project at Colorado State University since 1984. The original 1 August prediction scheme utilized several predictors, including measures of the stratospheric quasi-biennial oscillation (QBO), West African rainfall, El Nino–Southern Oscillation, and the sea level pressure anomaly and upper-tropospheric zonal wind anomalies in the Caribbean basin. The recent failure of the West African rainfall and QBO relationships with Atlantic hurricanes has led to a general degradation of the original 1 August forecast scheme in recent years. It was decided to revise the scheme using only surface data. The development of the National Centers for Environmental Prediction– National Center for Atmospheric Research reanalysis has provided a vast wealth of globally gridded meteorological and oceanic data from 1948 to the present. In addition, other datasets have been extended back even further (to 1900), which allows for a large independent dataset. These longer-period datasets allow for an extended period of testing of the new statistical forecast scheme. A new prediction scheme has been developed on data from 1949 to 1989 and then tested on two independent datasets. One of these datasets is the 16-yr period from 1990 to 2005, and the other dataset is from 1900 to 1948. This allows for an investigation of the statistical significance over various time periods. The statistical scheme shows remarkable stability over an entire century. The combination of these four predictors explains between 45% and 60% of the variance in net tropical cyclone activity over the following separate time periods: 1900–48, 1949–89, 1949–2005, and 1900–2005. The forecast scheme also shows considerable skill as a potential predictor for giving the probabilities of United States landfall. Large differences in U.S. major hurricane landfall are also observed between forecasts that call for active seasons compared with those that call for inactive seasons.

El Niño–Southern Oscillation’s Impact on Atlantic Basin Hurricanes and U.S. Landfalls

Abstract El Nino–Southern Oscillation (ENSO) has been shown in many previous papers to impact seasonal levels of Atlantic basin tropical cyclone activity. This paper revisits this relationship by examining a longer period (1900–2009) than has been examined in earlier analyses. Alterations in large-scale climate parameters, especially vertical wind shear, are shown to be the primary reasons why tropical cyclone activity in the Atlantic is reduced in El Nino years. Climate signals are found to be somewhat stronger in the Caribbean than for the remainder of the tropical Atlantic. The focus of the paper then shifts to U.S. landfalls, confirming previous research that U.S. landfalls are reduced in El Nino years. The reduction in landfall frequency is greater along the Florida peninsula and East Coast than it is along the Gulf Coast, especially for major hurricanes. The probability of each state being impacted by a hurricane and major hurricane is given for El Nino, La Nina, and neutral years. The most dramatic...

What Do Observational Datasets Say about Modeled Tropospheric Temperature Trends since 1979

Updated tropical lower tropospheric temperature datasets covering the period 1979–2009 are presented and assessed for accuracy based upon recent publications and several analyses conducted here. We conclude that the lower tropospheric temperature (TLT) trend over these 31 years is +0.09 ± 0.03 °C decade−1. Given that the surface temperature (Tsfc) trends from three different groups agree extremely closely among themselves (~ +0.12 °C decade−1) this indicates that the “scaling ratio” (SR, or ratio of atmospheric trend to surface trend: TLT/Tsfc) of the observations is ~0.8 ± 0.3. This is significantly different from the average SR calculated from the IPCC AR4 model simulations which is ~1.4. This result indicates the majority of AR4 simulations tend to portray significantly greater warming in the troposphere relative to the surface than is found in observations. The SR, as an internal, normalized metric of model behavior, largely avoids the confounding influence of short-term fluctuations such as El Ninos which make direct comparison of trend magnitudes less confident, even over multi-decadal periods.

The Influence of Natural Climate Variability on Tropical Cyclones, and Seasonal Forecasts of Tropical Cyclone Activity

In the first part of this chapter, we give a review of the relationship of climate and tropical cyclones on various time scales, from intra-seasonal to decadal. The response of tropical cyclone activity to natural modes of variability, such as El Niño-Southern Oscillation and the Madden Julian Oscillation in various regions of the world are discussed. Genesis location, track types and intensity of tropical cyclones are influenced by these modes of variability. In the second part, a review of the state of the art of seasonal tropical cyclone forecasting is discussed. The two main techniques currently used to produce tropical cyclone seasonal forecasts (statistical and dynamical) are discussed, with a focus on operational forecasts.

Forecasting September Atlantic Basin Tropical Cyclone Activity

September is the most active month for Atlantic basin tropical cyclone activity with about 50% of all hurricane activity occurring during this month. Utilizing National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) reanalysis data, a prediction scheme for forecasting September tropical cyclone activity has been developed. Based on hindcasting results from 1950 to 2000, 30%‐75% of the variance for most tropical cyclone parameters can be hindcast by the end of July. This hindcast skill improves to 45%‐ 75% by the end of August. Similarly, cross-validated hindcast skill explains from 20% to 65% for most variables by the end of July, improving to 30%‐65% by the end of August. Simple least squared linear regression was utilized to calculate hindcast skill, and variables were selected that explained the largest degree of variance when combined with the other predictors in the scheme. These predictors tend to be global in nature and include zonal and meridional wind at 200 and 1000 mb and sea level pressure measurements at various global locations.

The Madden–Julian Oscillation’s Impacts on Worldwide Tropical Cyclone Activity

The 30‐60-day Madden‐Julian oscillation (MJO) has been documented in previous research to impact tropicalcyclone(TC) activityfor varioustropicalcyclone basinsaroundthe globe.TheMJO modulateslargescale convective activity throughout the tropics, and concomitantly modulates other fields known to impact tropicalcycloneactivitysuchasverticalwindshear,midlevelmoisture,verticalmotion,andsealevelpressure. The Atlantic basin typically shows the smallest modulations in most large-scale fields of any tropical cyclone basins; however, it still experiences significant modulations in tropical cyclone activity. The convectively enhanced phases of the MJO and the phases immediately following them are typically associated with aboveaverage tropical cyclone frequency for each of the global TC basins, while the convectively suppressed phases of the MJO are typically associated with below-average tropical cyclone frequency. The number of rapid intensification periods are also shown to increase when the convectively enhanced phase of the MJO is impacting a particular tropical cyclone basin.

The Influence of El Nino-Southern Oscillation and the Atlantic Multidecadal Oscillation on Caribbean Tropical Cyclone Activity

Abstract Caribbean basin tropical cyclone activity shows significant variability on interannual as well as multidecadal time scales. Comprehensive statistics for Caribbean hurricane activity are tabulated, and then large-scale climate features are examined for their impacts on this activity. The primary interannual driver of variability is found to be El Nino–Southern Oscillation, which alters levels of activity due to changes in levels of vertical wind shear as well as through column stability. Much more activity occurs in the Caribbean with La Nina conditions than with El Nino conditions. On the multidecadal time scale, the Atlantic multidecadal oscillation is shown to play a significant role in Caribbean hurricane activity, likely linked to its close relationship with multidecadal alterations in the size of the Atlantic warm pool and the phase of the Atlantic meridional mode. When El Nino–Southern Oscillation and the Atlantic multidecadal oscillation are examined in combination, even stronger relations...