The TUTT Log is being maintained by Owen Shieh as part of his Ph.D. dissertation research at the University of Hawaii in Honolulu, Hawaii, in collaboration with the NOAA Earth System Research Laboratory in Boulder, Colorado and the Joint Typhoon Warning Center in Pearl Harbor, Hawaii. This three-way collaboration is being gratefully supported by the NSF Graduate Research Fellowship Program and the U.S. Pacific Command (USPACOM) Student Volunteer Internship Program. Many thanks to Dr. Bin Wang, Dr. Gary Barnes, Dr. Michael Bell, and Dr. Michael Fiorino for their advice as Ph.D. committee members. Special acknowledgement goes to Dr. Michael Fiorino at NOAA for providing computing and technical support for the tracker code, to Mr. Matthew Kucas at JTWC for his operational guidance, and to Ms. Ramona Ferreyra at USPACOM for administrative support. The primary author of The TUTT Log, Owen Shieh, may be contacted at oshieh@hawaii.edu.


The Tropical Upper-Tropospheric Trough (TUTT) is a semi-permanent, mid-oceanic feature of the monthly mean climatological tropical circulation. Within these troughs, concentrated areas of vorticity often develop, which persist as upper-tropospheric, cold-core cyclones, or “TUTT cells” (TUTTcs). Since the early years of atmospheric streamline analyses over the tropical and subtropical oceans, the TUTT has been observed to play an important role in the synoptic and large-scale interactions between the tropics and mid-latitudes. Tropical cyclones (TCs) are routinely influenced by upper-tropospheric phenomena, which have been shown to affect TC development and behavior, particularly TC intensity change. Operational TC forecasters have frequently expressed uncertainty in TC intensity forecasts when a TUTT or TUTTc is nearby.

As we seek to advance our understanding of TCs and to improve TC track and intensity forecasting in an era of high-resolution global modeling, interactions between TCs and TUTTcs must be objectively quantified. There have been many studies about mid-latitude upper-tropospheric trough/low interaction with TCs, but few have focused on TUTTs/TUTTcs. It is evident that the westward motion of TUTTcs and their separation from mid-latitude westerlies by the subtropical ridge can contribute to their longevity and subsequent interaction time with TCs. Furthermore, TCs are typically recurving in the case of mid-latitude trough interaction, whereas TUTTc interaction may occur at lower latitudes, where other conditions (e.g., sea surface temperatures, ocean heat content) support more rapid intensification. To better understand these relationships, an objective TUTTc tracker is currently being developed for use with NWP analyses, forecasts, and climate simulations. The tracker will isolate TUTTcs based on temperature/height/moisture/ozone anomalies alongside vorticity maxima. From this, a TC-TUTTc climatology will be generated, and calculations of model track, intensity, and longevity of TUTTcs will be performed. Subsequent quantification of TC intensity forecast degredation as a function of TC-TUTTc separation will allow for inter-basin comparisons and practical applications to TC forecasting.


This TUTT Log was created to provide a daily record of the TUTT and TUTTc activity in the western North Pacific (WPAC) and eastern North Pacific (EPAC), regions where the TUTT is climatologically most prevalent. Upper-tropospheric, cold-core lows come in many different forms. Those that persist in the climatological TUTT axis equatorward of the upper-tropospheric subtropical ridge are qualitatively considered as TUTTcs for the purposes of this log. Approximately once-daily TUTT/TUTTc summaries of a descriptive and qualitative nature are posted. All dates and times are in Zulu. TUTTcs are numbered and referenced in approximate chronological order, with a number assigned to the prefix “C” (e.g., C1, C2, C3). Each post is tagged based on any mention of TUTTc type or TC-TUTT interaction within the text of that entry, regardless of whether the discussion is about a past, present, or future event. TUTTc type is determined with regard to its genesis mechanism. However, once a TUTTc is mature, it will not necessarily be tagged with its genesis type for the duration of its lifetime. The TUTTc types are categorized as follows:

  • “Cut-Off” TUTTcs – Cases where a TUTTc originated from a cut-off circulation in the mid-latitude westerlies. Whether these cut-off cases are truly TUTTcs – rather than simply mid-latitude cold-core lows – is debatable, but are included here if they eventually propagate through the TUTT axis south of the upper-tropospheric subtropical ridge (STR).
  • “Shear-Induced” TUTTcs – Cases where a TUTTc originated in-situ in the vicinity of the climatological TUTT axis to the south of the STR, possibly as a result of barotropic instabilities.
  • “TC-Induced” TUTTcs – Cases where a TUTTc originated to the east of existing TCs, as described in Ferreira and Schubert (1999).

When a TC-TUTT interaction is described in a particular entry, the nature of the interaction is subjectively tagged as follows:

  • Favorable TC-TUTTcs – Cases where a TC-TUTTc interaction has likely contributed to TC intensification.
  • Unfavorable TC-TUTTcs – Cases where a TC-TUTTc interaction has likely contributed to TC weakening.

These categories, located in the drop-down menus above, together with the TUTT Log text search and calendar functions, will enable quick and easy navigation of TUTT and TUTTc events throughout the North Pacific. Ultimately, this log will enhance our understanding of typical synoptic patterns and serve as a tool to identify special cases with regard to the behavior of TUTTs, TUTTcs, an TCs. This will aid in the process of developing an objective method to define and detect TUTTs and TUTTcs for the benefit of TC intensity forecasting.


GFS model output graphics are courtesy of Dr. Michael Fiorino’s WxMap2, developed at the NOAA Earth System Research Laboratory. The satellite-derived winds and the header image are provided by CIMSS at the University of Wisconsin. The MTSAT visible image that serves as the background of The TUTT Log is courtesy of The Digital Typhoon archives. Other images used throughout the log are credited in the box that pops up when you mouse-over each of the images.

NOTE: All the posts contained within this TUTT Log are experimental, subjective, and intended for research purposes only. They are meant to be brief and to serve as quick references only – not to be deemed comprehensive synoptic discussions.


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