Tropical Cyclone Formation Alert (TCFA): purpose, issuance, and uses Tropical cyclone formation alert Overview of the Tropical Cyclone Formation Alert: what it is, which U.S. Navy centers issue it, typical criteria and content, how it is used, and how it differs from related adviso…
Tropical cyclone scales and category systems Tropical cyclone scales Overview of how tropical cyclones are classified worldwide, major scales (Saffir–Simpson, Australian), measurement differences, history, uses, limitations, and notable distinctions…
Tropical Depression One (2009) Overview and meteorological summary of Tropical Depression One, the first cyclone of the 2009 Atlantic hurricane season, its development, impacts, and significance as an early-seas…
Tropical Depression Seven (2003) A short-lived, weak tropical depression that formed near the northeast Florida coast on July 25, 2003, moved ashore in Georgia and produced primarily heavy rain across parts of the…
Tropical Storm Agatha (2010) A May 2010 Eastern Pacific storm whose heavy rains produced catastrophic flooding and landslides across Central America, killing roughly 190 people and causing widespread damage es…
Tropical Storm Alberto (1988) Tropical Storm Alberto was the first named storm of the 1988 Atlantic season, forming unusually far north and moving rapidly northeast; it produced only light rain and wind and cau…
Tropical Storm Alberto (1994): Flooding and impact in the southeastern United States Tropical Storm Alberto (1994) Tropical Storm Alberto (1994) was a slow-moving Atlantic cyclone that produced catastrophic rainfall and flooding across parts of Florida, Georgia and Alabama, causing dozens of de…
Tropical Storm Aletta (2006) Early-season Eastern Pacific tropical storm that formed off Guerrero, Mexico in late May 2006. It was the first named cyclone of the 2006 Pacific season, produced coastal rain and…
Tropical Storm Ana (2003): an uncommon Atlantic April cyclone Tropical Storm Ana (2003) Tropical Storm Ana formed in April 2003 west of Bermuda as a subtropical cyclone, transitioned to a tropical storm, and became extratropical on April 24. It produced light rain, ro…
Tropical Storm Arlene (2005) Tropical Storm Arlene was the first named storm of the 2005 Atlantic season. It formed in early June, reached near-hurricane strength, made landfall in western Florida, and caused…
Tropical Storm Beryl (2006): formation, track, and impacts Tropical Storm Beryl (2006) Summary of Tropical Storm Beryl (July 2006): meteorological history, path, impacts on Nantucket, New England and Atlantic Canada, preparations and aftermath.
Tropical Storm Bret (1993) A deadly tropical storm in early August 1993 that produced heavy rains, flooding and landslides across northern South America and parts of Central America, causing nearly 200 death…
Tropical Storm Bret (2005) Brief account of Tropical Storm Bret, a short-lived 2005 Atlantic tropical storm that formed in the Bay of Campeche, made quick landfall on Mexico, and caused limited but deadly im…
Tropical Storm Chris (2006) A short-lived Atlantic tropical storm during late July–early August 2006 that formed from a tropical wave, reached peak winds near 65 mph, skirted the northern Caribbean and dissip…
Tropical Storm Claudette (1979) A destructive late-July 1979 Atlantic tropical storm that produced record rainfall in Texas, heavy damage and flooding, and was an early notable cyclone of the 1979 season.
Tropical Storm Claudette (2009) A concise account of Tropical Storm Claudette (2009): formation, path, impacts on the Florida Panhandle and Alabama, associated tornado and drowning, and its place in the 2009 Atla…
Tropical Storm Cristobal (2002) An overview of Tropical Storm Cristobal (2002): a short-lived Atlantic tropical storm that stayed mostly over open water, produced rain in Bermuda and dangerous surf that led to dr…
Tropical Storm Debby (2006): formation, path, and meteorological summary Tropical Storm Debby (2006) A concise overview of Tropical Storm Debby (2006): origin near Africa, life cycle, peak intensity, weakening by wind shear, forecasts and final dissipation over the northern Atlant…
Tropical Storm Doria (August 1971) Tropical Storm Doria Tropical Storm Doria formed August 20, 1971; it moved north of the Greater Antilles and up the U.S. East Coast, producing heavy rain, an F1 tornado, and about $147.6 million in dam…
Tropical Storm Erin (2007) A summary of Tropical Storm Erin (August 2007): formation, track, impacts in Texas and Oklahoma, and its place in the 2007 Atlantic hurricane season.
Tropical Storm Gabrielle (2007) Overview of Tropical Storm Gabrielle (2007): its formation as a subtropical cyclone, brief intensification to a tropical storm, landfall in eastern North Carolina, impacts, and dis…
Tropical Storm Gordon (2018) A brief account of Tropical Storm Gordon, which formed in early September 2018, crossed southern Florida, moved into the Gulf of Mexico, and prompted coastal warnings across the no…
Tropical Storm Ingrid (2007) Short-lived Atlantic tropical storm in September 2007 that formed from Tropical Depression Eight, weakened by wind shear, and produced light rains in parts of the northeastern Cari…
Tropical Storm Jerry (1995) Tropical Storm Jerry was a short-lived but deadly storm of the very active 1995 Atlantic hurricane season, making landfall in Florida and causing eight deaths and about $40 million…
Tropical Storm Jerry (2007) Short-lived 2007 Atlantic tropical storm that formed in the north-central Atlantic, spent part of its brief life as a subtropical cyclone and remained well away from land.
Tropical Storm Lee (2005) A short-lived, weak tropical cyclone in the central Atlantic during late August–early September 2005 that briefly reached tropical storm strength and remained over open water.
Tropical Storm Olga (2007) A late-season subtropical storm that formed in December 2007, struck Hispaniola and caused deadly flooding in Puerto Rico, the Dominican Republic and Haiti before dissipating.
Tropical Storm Peter (2003) A late-season Atlantic cyclone that evolved from an extratropical system and briefly reached 70 mph (110 km/h) on December 9, 2003 before weakening.
Tropical Upper Tropospheric Trough (TUTT) Tropical Upper Tropospheric Trough A TUTT is an upper‑tropospheric trough in the tropics that influences convection and tropical cyclone behavior by altering upper‑level flow, shear, and outflow.
Tropopause — atmospheric boundary between troposphere and stratosphere Tropopause The tropopause is the transition layer between the weather-active troposphere and the stratified stratosphere. Its height and strength affect weather, climate, ozone distribution a…
Troposphere: Earth's Lowest Atmospheric Layer — Structure, Composition, and Role Troposphere The troposphere is the lowest layer of Earth's atmosphere where weather occurs. This article explains its structure, composition, temperature profile, role in climate and aviation,…
Trough (geology): definition, formation, types, and significance Trough (geology) A geological trough is a linear depression formed by tectonic or erosional processes. This article explains its characteristics, formation mechanisms, types (including oceanic trou…
Trough (meteorology) A trough is an elongated area of relatively low atmospheric pressure that influences wind patterns, cloudiness, precipitation, and storm development across tropical and mid-latitud…
Tseax River Cone (Aiyansh Volcano) Tseax River Cone A basaltic cinder cone in northwestern British Columbia whose late 18th-century eruption buried landscapes and caused roughly 2,000 deaths; now preserved as Nisga'a Memorial Lava B…
Tsunami: causes, behavior, impacts and preparedness Tsunami An extended overview of tsunamis: what they are, how they form, their typical characteristics, notable events, warning systems, preparedness, and how megatsunamis differ.
Tufa — porous carbonate rock formed by calcium carbonate precipitation Tufa Tufa is a soft, porous variety of limestone formed when carbonate minerals precipitate from ambient-temperature water. It differs from travertine and from volcanic tuff and has eco…
Tuff: consolidated volcanic ash — formation, varieties, and uses Tuff Tuff is a rock formed from volcanic ash that has been compacted and cemented. This article explains how tuff forms, its main types and properties, historic and modern uses, and how…
Tungurahua — an active Ecuadorian stratovolcano Tungurahua Tungurahua is an active stratovolcano in the Ecuadorian Andes. Named “Throat of Fire,” it reawakened in 1999 and has been a prominent source of ash, pyroclastic flows and evacuatio…
Unconformity (geology): definition, types, and significance Unconformity An unconformity is a surface in the rock record marking a gap in time caused by non-deposition or erosion. This article explains types, formation, historical examples, and why they…
Underwater: the environment beneath a water surface Underwater Overview of underwater environments: seafloor forms and depth zones, life and adaptations, human uses and exploration, and notable deep-ocean features.
Uniformitarianism: Principles, History, and Modern Significance Uniformitarianism Uniformitarianism is the geological principle that Earth's features result from long-term processes consistent with present-day natural laws. This article explains its principles,…
United States Geological Survey (USGS) United States Geological Survey The USGS is the U.S. Department of the Interior's scientific agency that studies landscape, water, biological resources, minerals and natural hazards and provides open data and map…
Upper Cretaceous: Geological Epoch of Chalk Seas, Dinosaur Faunas, and the K–Pg Extinction Upper Cretaceous Upper Cretaceous (c. 100.5–66 Ma): the final Cretaceous epoch defined by extensive chalk seas, diverse dinosaur and marine faunas, rising flowering plants, and ending with the K–Pg…
Upper Jurassic (Late Jurassic Epoch) Upper Jurassic The Upper Jurassic, or Late Jurassic, lasted from about 163.5 to 145 million years ago. It featured widespread shallow seas, warm climates, huge sauropods, diverse marine reptiles…
Upper Triassic (Late Triassic epoch) Upper Triassic The Upper Triassic (Late Triassic) is the final epoch of the Triassic Period (≈237–201.3 Ma), notable for early dinosaur diversification, diverse marine reptiles, shifting climates…
Ur (supercontinent): an ancient continental nucleus Ur (supercontinent) Ur was a proposed early continental nucleus that assembled in the Archaean and later contributed cratonic fragments to larger supercontinents such as Rodinia and Pangaea.
Uranium mining: methods, uses, risks, and global production Uranium mining Overview of uranium mining, major producers, extraction methods, processing into nuclear fuel, environmental and health impacts, market influences, and regulatory responses.
Uranium–lead dating (U–Pb): principles, methods, and applications Uranium-lead dating Uranium–lead dating uses decay of 238U and 235U to lead isotopes to determine geologic ages from ~1 million to >4.5 billion years with high precision; widely applied to zircon and…
