EASTERN PACIFIC SEASON MAP
1970 Pacific hurricane season
20 recorded storms from May 30, 1970 to Nov 6, 1970
Last updated
The 1970 Pacific hurricane season produced 20 tropical storms, 5 hurricanes and no major hurricanes. Storms came thick and fast from late May through August, and Hurricane Patricia became the strongest of the year with a 95 kt peak in October. The deadliest effects fell far inland, where moisture from Tropical Storm Norma fed record Labor Day rains in Arizona. Read more
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| Adele | – | 86 | Cat 1 | — | 2,250 |
|---|---|---|---|---|---|
| Blanca | – | 58 | Tropical storm | — | 230 |
| Connie | – | 52 | Tropical storm | — | 580 |
| Eileen | – | 46 | Tropical storm | — | 850 |
| Francesca | – | 98 | Cat 2 | 991 | 2,510 |
| Gretchen | – | 52 | Tropical storm | 1009 | 1,000 |
| Helga | – | 58 | Tropical storm | — | 670 |
| Ione | – | 52 | Tropical storm | — | 1,100 |
| Ione | – | 58 | Tropical storm | — | 210 |
| Joyce | – | 58 | Tropical storm | — | 1,110 |
| Therese | – | 46 | Tropical storm | 990 | 2,980 |
| Kristen | – | 52 | Tropical storm | — | 1,040 |
| Lorraine | – | 98 | Cat 2 | 963 | 3,210 |
| Maggie | – | 58 | Tropical storm | — | 1,960 |
| Norma | – | 58 | Tropical storm | 992 | 1,190 |
| Dot | – | 81 | Cat 1 | — | 1,350 |
| Orlene | – | 63 | Tropical storm | — | 350 |
| Patricia | – | 109 | Cat 2 | 972 | 2,390 |
| Rosalie | – | 52 | Tropical storm | 1006 | 600 |
| Selma | – | 69 | Tropical storm | 995 | 1,110 |
20 storms with an IBTrACS 1970 hurricane season record. Tracks are the archived center positions, first observation May 30, 1970, last Nov 6, 1970.
Tropical-stage US-agency wind of 39 mph or more
74 mph or more, one-minute sustained
110 mph or more, Saffir–Simpson scale
158 mph or more at any tropical-stage observation
109 mph
Lorraine, Aug 22, 1970
Lorraine, full archive record
Mapped, but outside the counts above
SEASON HISTORY
Counting a crowded year
The current best track describes 21 tropical cyclones, 18 tropical storms and 4 hurricanes in the eastern Pacific, plus a hurricane and a depression in the central Pacific. The site's 20 tropical storms and 5 hurricanes come from a different tally. It adds central Pacific Hurricane Dot and Tropical Storm Therese, which crossed in from the western Pacific, and it lists the two storms both named Ione as separate systems. Accumulated cyclone energy came to 78.3.
Hurricane Adele opened the season on 30 May and reached hurricane strength on 1 June before a hostile environment wore it down at sea. Blanca, Connie and Eileen followed in June, and Eileen came ashore in western Mexico near the end of the month at its 45 mph peak. A system named Dolores turned out, after reconnaissance and later analysis, to have been only a depression.
Storms hidden under cloud
Hurricane Francesca formed on 1 July, and a ship near its center on 3 July measured winds near 100 mph. A cap of high cloud sat over the eye for days, so forecasters could not see how strong the storm was from above. The archive gives Francesca an 85 kt peak and 991 mb. Tropical Storm Joyce later in July hid its low-level center under a similar cirrus cap.
Late July produced an odd pair. A depression off southern Mexico split into two systems, and forecasters called both Ione because they treated them as one storm at the time. The ship Kanikawa Maru met the eastern Ione on 24 July with 48 kt winds and 15-foot seas; the western one faded as the larger circulation of its twin reached it.
Lorraine, Maggie and Dot toward Hawaii
Hurricane Lorraine formed south of Mexico on 16 August and became the longest-tracked storm of the year at 276 recorded hours. It peaked on 22 August at 85 kt in the archive, and its 963 mb pressure was the lowest of the season. The Central Pacific Hurricane Center estimated winds nearer 115 mph. Dry air finished Lorraine on 27 August.
Tropical Storm Maggie formed west-southwest of Lorraine and passed about 80 miles south of the island of Hawaii on 25 August. A westward turn spared the island a direct hit, but Maggie dropped 10 to 15 inches of rain on the windward side and brought heavy surf. Hurricane Dot, which may have grown from Maggie's remains, formed northwest of Hawaii on 1 September and became a hurricane near 35°N on 3 September, then the highest latitude at which a storm had reached hurricane strength east of the date line.
Norma and the Labor Day floods
Tropical Storm Norma formed on 31 August, strengthened quickly and headed out to sea before weakening. Its circulation pumped humid, unstable air into a large extratropical low over Arizona, and record rain fell across the state from 4 to 6 September as Norma dissipated. The rains killed 22 people, including 14 in a flash flood on one creek, and damage of more than $1 million in 1970 dollars.
Tropical Storm Orlene struck eastern Oaxaca on 8 September after a short northeastward track. Its peak winds reached about 65 mph.
Patricia and the late season
Hurricane Patricia formed on 4 October, peaked at 95 kt on 8 October with a pressure of 972 mb in the archive, and stayed at sea. Rosalie followed later in October, and Tropical Storm Selma closed the year, meandering southwest of Mexico from 1 November until it dissipated a week later.
Six names, among them Norma, Patricia and Selma, were used for the first time. The name Adele was later retired without explanation and replaced with Aletta for 1974.
Further reading
QUICK ANSWERS
The 1970 season in brief
How many hurricanes were there in the 1970 Pacific hurricane season?
The archive records 5 hurricanes (one-minute winds of 74 mph or more) among 20 tropical storms, with 0 major hurricanes reaching 110 mph. Counts use US-agency winds during the tropical stage.
What was the strongest storm of the 1970 Pacific hurricane season?
Patricia, with a peak one-minute sustained wind of 109 mph (Category 2) on Oct 8, 1970, 06:00 PM UTC and a minimum central pressure of 972 mb.
How many Category 5 storms were there in 1970?
None. No storm in the 1970 Pacific hurricane season reached Category 5 on the Saffir–Simpson one-minute wind scale in the archive.
When did the 1970 Pacific hurricane season start and end?
The first tropical-stage observation is on May 30, 1970 and the last on Nov 6, 1970, from 20 tracked storms in the archive.
What was the first hurricane of the 1970 Pacific hurricane season?
Adele, which reached hurricane strength (74 mph) on Jun 1, 1970, 12:00 AM UTC.
METHODOLOGY
Data sources and limitations
The map and totals are generated from NOAA's IBTrACS v04r01 archive. A storm belongs to this page when the archive lists it in the Eastern Pacific basin for the 1970 season, so a December storm whose track ends in January stays with its season. Storms that cross between basins appear on the page of their archive basin only.
Counts use US-agency one-minute winds during the tropical stage: 34 kt for a tropical storm, 64 kt for hurricane strength and 96 kt for major intensity, on the Saffir–Simpson scale in every basin. Local agencies classify storms differently, and official season summaries can differ from the archive. Accumulated cyclone energy sums squared winds at six-hourly synoptic times, counting observations in the calendar year. Storms with no US-agency wind are mapped but cannot enter the counts.
The map frame is the same for every Eastern Pacific season, so a track that leaves it is cut at the edge. Lines show each storm's center, not its size, rainfall or flood extent. Coastlines use Natural Earth's 1:10m land data.
Archive retrieved
NOAA IBTrACS archive and Field documentation
Sources & methodology